silverstripe-framework/model/DataObject.php

<?php
/**
 * A single database record & abstract class for the data-access-model.
 *
 * <h2>Extensions</h2>
 *
 * See {@link Extension} and {@link DataExtension}.
 * 
 * <h2>Permission Control</h2>
 * 
 * Object-level access control by {@link Permission}. Permission codes are arbitrary
 * strings which can be selected on a group-by-group basis.
 * 
 * <code>
 * class Article extends DataObject implements PermissionProvider {
 * 	static $api_access = true;
 * 	
 * 	public function canView($member = false) {
 * 		return Permission::check('ARTICLE_VIEW');
 * 	}
 * 	public function canEdit($member = false) {
 * 		return Permission::check('ARTICLE_EDIT');
 * 	}
 * 	public function canDelete() {
 * 		return Permission::check('ARTICLE_DELETE');
 * 	}
 * 	public function canCreate() {
 * 		return Permission::check('ARTICLE_CREATE');
 * 	}
 * 	public function providePermissions() {
 * 		return array(
 * 			'ARTICLE_VIEW' => 'Read an article object',
 * 			'ARTICLE_EDIT' => 'Edit an article object',
 * 			'ARTICLE_DELETE' => 'Delete an article object',
 * 			'ARTICLE_CREATE' => 'Create an article object',
 * 		);
 * 	}
 * }
 * </code> 
 *
 * Object-level access control by {@link Group} membership: 
 * <code>
 * class Article extends DataObject {
 * 	static $api_access = true;
 * 	
 * 	public function canView($member = false) {
 * 		if(!$member) $member = Member::currentUser();
 *		return $member->inGroup('Subscribers');
 * 	}
 * 	public function canEdit($member = false) {
 * 		if(!$member) $member = Member::currentUser();
 *		return $member->inGroup('Editors');
 * 	}
 * 	
 * 	// ...
 * }
 * </code>
 * 
 * If any public method on this class is prefixed with an underscore, 
 * the results are cached in memory through {@link cachedCall()}.
 * 
 * 
 * @todo Add instance specific removeExtension() which undos loadExtraStatics()
 *  and defineMethods()
 * 
 * @package sapphire
 * @subpackage model
 */
class DataObject extends ViewableData implements DataObjectInterface, i18nEntityProvider {
	
	/**
	 * Human-readable singular name.
	 * @var string
	 */
	public static $singular_name = null;
	
	/**
	 * Human-readable pluaral name
	 * @var string
	 */
	public static $plural_name = null;
	
	/**
	 * Allow API access to this object?
	 * @todo Define the options that can be set here
	 */
	public static $api_access = false;
	
	public static
		$cache_has_own_table       = array(),
		$cache_has_own_table_field = array();
	
	/**
	 * True if this DataObject has been destroyed.
	 * @var boolean
	 */
	public $destroyed = false;
	
	/**
	 * The DataModel from this this object comes
	 */
	protected $model;
	
	/**
	 * Data stored in this objects database record. An array indexed by fieldname. 
	 * 
	 * Use {@link toMap()} if you want an array representation
	 * of this object, as the $record array might contain lazy loaded field aliases.
	 * 
	 * @var array
	 */
	protected $record;

	/**
	 * An array indexed by fieldname, true if the field has been changed.
	 * Use {@link getChangedFields()} and {@link isChanged()} to inspect
	 * the changed state.
	 * 
	 * @var array
	 */
	private $changed;

	/**
	 * The database record (in the same format as $record), before
	 * any changes.
	 * @var array
	 */
	protected $original;

	/**
	 * The one-to-one, one-to-many and many-to-one components
	 * indexed by component name.
	 * @var array
	 */
	protected $components;
	
	/**
	 * Used by onBeforeDelete() to ensure child classes call parent::onBeforeDelete()
	 * @var boolean
	 */
	protected $brokenOnDelete = false;
	
	/**
	 * Used by onBeforeWrite() to ensure child classes call parent::onBeforeWrite()
	 * @var boolean
	 */
	protected $brokenOnWrite = false;
	
	/**
	 * Should dataobjects be validated before they are written?
	 */
	private static $validation_enabled = true;
	
	/**
	 * Returns when validation on DataObjects is enabled.
	 * @return bool
	 */
	static function get_validation_enabled() {
		return self::$validation_enabled;
	}
	
	/**
	 * Set whether DataObjects should be validated before they are written.
	 * @param $enable bool
	 * @see DataObject::validate()
	 */
	static function set_validation_enabled($enable) {
		self::$validation_enabled = (bool) $enable;
	}

	/**
	 * Return the complete map of fields on this object, including "Created", "LastEdited" and "ClassName".
	 * See {@link custom_database_fields()} for a getter that excludes these "base fields".
	 *
	 * @param string $class
	 * @return array
	 */
	public static function database_fields($class) {
		if(get_parent_class($class) == 'DataObject') {
			return array_merge (
				array (
					'ClassName'  => "Enum('" . implode(', ', ClassInfo::subclassesFor($class)) . "')",
					'Created'    => 'SS_Datetime',
					'LastEdited' => 'SS_Datetime'
				),
				self::custom_database_fields($class)
			);
		}

		return self::custom_database_fields($class);
	}

	/**
	 * Get all database columns explicitly defined on a class in {@link DataObject::$db} 
	 * and {@link DataObject::$has_one}. Resolves instances of {@link CompositeDBField} 
	 * into the actual database fields, rather than the name of the field which 
	 * might not equate a database column.
	 * 
	 * Does not include "base fields" like "ID", "ClassName", "Created", "LastEdited",
	 * see {@link database_fields()}.
	 * 
	 * @uses CompositeDBField->compositeDatabaseFields()
	 *
	 * @param string $class
	 * @return array Map of fieldname to specification, similiar to {@link DataObject::$db}.
	 */
	public static function custom_database_fields($class) {
		$fields = Object::uninherited_static($class, 'db');
		
		foreach(self::composite_fields($class, false) as $fieldName => $fieldClass) {
			// Remove the original fieldname, its not an actual database column
			unset($fields[$fieldName]);
			
			// Add all composite columns
			$compositeFields = singleton($fieldClass)->compositeDatabaseFields();
			if($compositeFields) foreach($compositeFields as $compositeName => $spec) {
				$fields["{$fieldName}{$compositeName}"] = $spec;
			}
		}
		
		// Add has_one relationships
		$hasOne = Object::uninherited_static($class, 'has_one');
		if($hasOne) foreach(array_keys($hasOne) as $field) {
			$fields[$field . 'ID'] = 'ForeignKey';
		}
		
		return (array)$fields;
	}
	
	private static $_cache_custom_database_fields = array();
	
	
	/**
	 * Returns the field class if the given db field on the class is a composite field.
	 * Will check all applicable ancestor classes and aggregate results.
	 */
	static function is_composite_field($class, $name, $aggregated = true) {
		if(!isset(self::$_cache_composite_fields[$class])) self::cache_composite_fields($class);
		
		if(isset(self::$_cache_composite_fields[$class][$name])) {
			return self::$_cache_composite_fields[$class][$name];
			
		} else if($aggregated && $class != 'DataObject' && ($parentClass=get_parent_class($class)) != 'DataObject') {
			return self::is_composite_field($parentClass, $name);
		}
	}

	/**
	 * Returns a list of all the composite if the given db field on the class is a composite field.
	 * Will check all applicable ancestor classes and aggregate results.
	 */
	static function composite_fields($class, $aggregated = true) {
		if(!isset(self::$_cache_composite_fields[$class])) self::cache_composite_fields($class);
		
		$compositeFields = self::$_cache_composite_fields[$class];
		
		if($aggregated && $class != 'DataObject' && ($parentClass=get_parent_class($class)) != 'DataObject') {
			$compositeFields = array_merge($compositeFields, 
				self::composite_fields($parentClass));
		}
		
		return $compositeFields;
	}

	/**
	 * Internal cacher for the composite field information
	 */
	private static function cache_composite_fields($class) {
		$compositeFields = array();
		
		$fields = Object::uninherited_static($class, 'db');
		if($fields) foreach($fields as $fieldName => $fieldClass) {
			// Strip off any parameters
			$bPos = strpos('(', $fieldClass);
			if($bPos !== FALSE) $fieldClass = substr(0,$bPos, $fieldClass);
			
			// Test to see if it implements CompositeDBField
			if(ClassInfo::classImplements($fieldClass, 'CompositeDBField')) {
				$compositeFields[$fieldName] = $fieldClass;
			}
		}
		
		self::$_cache_composite_fields[$class] = $compositeFields;
	}
	
	private static $_cache_composite_fields = array();
	

	/**
	 * Construct a new DataObject.
	 *
	 * @param array|null $record This will be null for a new database record.  Alternatively, you can pass an array of
	 * field values.  Normally this contructor is only used by the internal systems that get objects from the database.
	 * @param boolean $isSingleton This this to true if this is a singleton() object, a stub for calling methods.  Singletons
	 * don't have their defaults set.
	 */
	function __construct($record = null, $isSingleton = false, $model = null) {
		// Set the fields data.
		if(!$record) {
			$record = array(
				'ID' => 0,
				'ClassName' => get_class($this),
				'RecordClassName' => get_class($this)
			);
		}

		if(!is_array($record)) {
			if(is_object($record)) $passed = "an object of type '$record->class'";
			else $passed = "The value '$record'";

			user_error("DataObject::__construct passed $passed.  It's supposed to be passed an array,
			taken straight from the database.  Perhaps you should use DataObject::get_one instead?", E_USER_WARNING);
			$record = null;
		}

		// Convert PostgreSQL boolean values
		// TODO: Implement this more elegantly, for example by writing a more intelligent SQL SELECT query prior to object construction
		if(DB::getConn() instanceof PostgreSQLDatabase) {
			$this->class = get_class($this);
			foreach($record as $k => $v) {
				if($this->db($k) == 'Boolean' && $v == 'f') $record[$k] = '0';
			}
		}
		
		// TODO: MSSQL has a convert function that can do this on the SQL end. We just need a
		// nice way of telling the database how we want to get the value out on a per-fieldtype basis
		if(DB::getConn() instanceof MSSQLDatabase) {
			$this->class = get_class($this);
			foreach($record as $k => $v) {
				if($v) {
					if($k == 'Created' || $k == 'LastEdited') {
						$fieldtype = 'SS_Datetime';
					} else {
						$fieldtype = $this->db($k);
					}
				
					// MSSQLDatabase::date() uses datetime for the data type for "Date" and "SS_Datetime"
					switch($fieldtype) {
						case "Date":
							$v = preg_replace('/:[0-9][0-9][0-9]([ap]m)$/i', ' \\1', $v);
							$record[$k] = date('Y-m-d', strtotime($v));
							break;
					
						case "Datetime":
						case "SS_Datetime":
							$v = preg_replace('/:[0-9][0-9][0-9]([ap]m)$/i', ' \\1', $v);
							$record[$k] = date('Y-m-d H:i:s', strtotime($v));
							break;
					}
				}
			}
		}

		// Set $this->record to $record, but ignore NULLs
		$this->record = array();
		foreach($record as $k => $v) {
			// Ensure that ID is stored as a number and not a string
			// To do: this kind of clean-up should be done on all numeric fields, in some relatively
			// performant manner
			if($v !== null) {
				if($k == 'ID' && is_numeric($v)) $this->record[$k] = (int)$v;
				else $this->record[$k] = $v;
			}
		}
		$this->original = $this->record;

		// Keep track of the modification date of all the data sourced to make this page
		// From this we create a Last-Modified HTTP header
		if(isset($record['LastEdited'])) {
			HTTP::register_modification_date($record['LastEdited']);
		}

		parent::__construct();

		// Must be called after parent constructor
		if(!$isSingleton && (!isset($this->record['ID']) || !$this->record['ID'])) {
			$this->populateDefaults();
		}

		// prevent populateDefaults() and setField() from marking overwritten defaults as changed
		$this->changed = array();
		
		$this->model = $model ? $model : DataModel::inst();
	}
	
	/**
	 * Set the DataModel
	 */
	function setModel(DataModel $model) {
		$this->model = $model;
	}

	/**
	 * Destroy all of this objects dependant objects.
	 * You'll need to call this to get the memory of an object that has components or extensions freed.
	 */
	function destroy() {
		$this->extension_instances = null;
		$this->components = null;
		$this->destroyed = true;
		$this->record = null;
		$this->original = null;
		$this->changed = null;
		$this->flushCache(false);
	}

	/**
	 * Create a duplicate of this node.
	 * Note: now also duplicates relations.
	 *
	 * @param $doWrite Perform a write() operation before returning the object.  If this is true, it will create the duplicate in the database.
	 * @return DataObject A duplicate of this node. The exact type will be the type of this node.
	 */
	function duplicate($doWrite = true) {
		$className = $this->class;
		$clone = new $className( $this->record, false, $this->model );
		$clone->ID = 0;
		
		$clone->extend('onBeforeDuplicate', $this, $doWrite);
		if($doWrite) {
			$clone->write();
			$this->duplicateManyManyRelations($this, $clone);
		}
		$clone->extend('onAfterDuplicate', $this, $doWrite);
		
		return $clone;
	}

	/**
	 * Copies the many_many and belongs_many_many relations from one object to another instance of the name of object
	 * The destinationObject must be written to the database already and have an ID. Writing is performed automatically when adding the new relations.
	 *
	 * @param $sourceObject the source object to duplicate from
	 * @param $destinationObject the destination object to populate with the duplicated relations
	 * @return DataObject with the new many_many relations copied in
	 */
	protected function duplicateManyManyRelations($sourceObject, $destinationObject) {
		if (!$destinationObject || $destinationObject->ID < 1) user_error("Can't duplicate relations for an object that has not been written to the database", E_USER_ERROR);

		//duplicate complex relations
		// DO NOT copy has_many relations, because copying the relation would result in us changing the has_one relation
		// on the other side of this relation to point at the copy and no longer the original (being a has_one, it can
		// only point at one thing at a time). So, all relations except has_many can and are copied
		if ($sourceObject->has_one()) foreach($sourceObject->has_one() as $name => $type) {
			$this->duplicateRelations($sourceObject, $destinationObject, $name);
		}
		if ($sourceObject->many_many()) foreach($sourceObject->many_many() as $name => $type) { //many_many include belongs_many_many
			$this->duplicateRelations($sourceObject, $destinationObject, $name);
		}

		return $destinationObject;
	}

	/**
	 * Helper function to duplicate relations from one object to another
	 * @param $sourceObject the source object to duplicate from
	 * @param $destinationObject the destination object to populate with the duplicated relations
	 * @param $name the name of the relation to duplicate (e.g. members) 
	 */
	private function duplicateRelations($sourceObject, $destinationObject, $name) {
		$relations = $sourceObject->$name();
		if ($relations) {
			if ($relations instanceOf RelationList) {   //many-to-something relation
				if ($relations->Count() > 0) {  //with more than one thing it is related to
					foreach($relations as $relation) {
						$destinationObject->$name()->add($relation);
					}
				}
			} else {    //one-to-one relation
				$destinationObject->$name = $relations;
			}
		}
	}
	
	/**
	 * Set the ClassName attribute. {@link $class} is also updated.
	 * Warning: This will produce an inconsistent record, as the object
	 * instance will not automatically switch to the new subclass.
	 * Please use {@link newClassInstance()} for this purpose,
	 * or destroy and reinstanciate the record.
	 *
	 * @param string $className The new ClassName attribute (a subclass of {@link DataObject})
	 */
	function setClassName($className) {
		$className = trim($className);
		if(!$className || !is_subclass_of($className, 'DataObject')) return;

		$this->class = $className;
		$this->setField("ClassName", $className);
	}

	/**
	 * Create a new instance of a different class from this object's record.
	 * This is useful when dynamically changing the type of an instance. Specifically,
	 * it ensures that the instance of the class is a match for the className of the
	 * record. Don't set the {@link DataObject->class} or {@link DataObject->ClassName}
	 * property manually before calling this method, as it will confuse change detection.
	 * 
	 * If the new class is different to the original class, defaults are populated again
	 * because this will only occur automatically on instantiation of a DataObject if
	 * there is no record, or the record has no ID. In this case, we do have an ID but
	 * we still need to repopulate the defaults.
	 *
	 * @param string $newClassName The name of the new class
	 *
	 * @return DataObject The new instance of the new class, The exact type will be of the class name provided.
	 */
	function newClassInstance($newClassName) {
		$originalClass = $this->ClassName;
		$newInstance = new $newClassName(array_merge(
			$this->record,
			array(
				'ClassName' => $originalClass,
				'RecordClassName' => $originalClass,
			)
		), false, $this->model);
		
		if($newClassName != $originalClass) {
			$newInstance->setClassName($newClassName);
			$newInstance->populateDefaults();
			$newInstance->forceChange();
		}

		return $newInstance;
	}

	/**
	 * Adds methods from the extensions.
	 * Called by Object::__construct() once per class.
	 */
	function defineMethods() {
		parent::defineMethods();

		// Define the extra db fields - this is only necessary for extensions added in the
		// class definition.  Object::add_extension() will call this at definition time for
		// those objects, which is a better mechanism.  Perhaps extensions defined inside the
		// class def can somehow be applied at definiton time also?
		if($this->extension_instances) foreach($this->extension_instances as $i => $instance) {
			if(!$instance->class) {
				$class = get_class($instance);
				user_error("DataObject::defineMethods(): Please ensure {$class}::__construct() calls parent::__construct()", E_USER_ERROR);
			}
		}

		if($this->class == 'DataObject') return;

		// Set up accessors for joined items
		if($manyMany = $this->many_many()) {
			foreach($manyMany as $relationship => $class) {
				$this->addWrapperMethod($relationship, 'getManyManyComponents');
			}
		}
		if($hasMany = $this->has_many()) {

			foreach($hasMany as $relationship => $class) {
				$this->addWrapperMethod($relationship, 'getComponents');
			}

		}
		if($hasOne = $this->has_one()) {
			foreach($hasOne as $relationship => $class) {
				$this->addWrapperMethod($relationship, 'getComponent');
			}
		}
		if($belongsTo = $this->belongs_to()) foreach(array_keys($belongsTo) as $relationship) {
			$this->addWrapperMethod($relationship, 'getComponent');
		}
	}

	/**
	 * Returns true if this object "exists", i.e., has a sensible value.
	 * The default behaviour for a DataObject is to return true if
	 * the object exists in the database, you can override this in subclasses.
	 *
	 * @return boolean true if this object exists
	 */
	public function exists() {
		return ($this->record && $this->record['ID'] > 0);
	}

	/**
	 * Returns TRUE if all values (other than "ID") are
	 * considered empty (by weak boolean comparison).
	 * Only checks for fields listed in {@link custom_database_fields()}
	 * 
	 * @todo Use DBField->hasValue()
	 * 
	 * @return boolean
	 */
	public function isEmpty(){
		$isEmpty = true;
		$customFields = self::custom_database_fields(get_class($this));
		if($map = $this->toMap()){
			foreach($map as $k=>$v){
				// only look at custom fields
				if(!array_key_exists($k, $customFields)) continue;
				
				$dbObj = ($v instanceof DBField) ? $v : $this->dbObject($k);
				$isEmpty = ($isEmpty && !$dbObj->hasValue());
			}
		}
		return $isEmpty;
	}

	/**
	 * Get the user friendly singular name of this DataObject.
	 * If the name is not defined (by redefining $singular_name in the subclass),
	 * this returns the class name.
	 *
	 * @return string User friendly singular name of this DataObject
	 */
	function singular_name() {
		if(!$name = $this->stat('singular_name')) {
			$name = ucwords(trim(strtolower(preg_replace('/_?([A-Z])/', ' $1', $this->class))));
		}
		
		return $name;
	}

	/**
	 * Get the translated user friendly singular name of this DataObject
	 * same as singular_name() but runs it through the translating function
	 *
	 * Translating string is in the form:
	 *     $this->class.SINGULARNAME
	 * Example:
	 *     Page.SINGULARNAME
	 *
	 * @return string User friendly translated singular name of this DataObject
	 */
	function i18n_singular_name() {
		return _t($this->class.'.SINGULARNAME', $this->singular_name());
	}

	/**
	 * Get the user friendly plural name of this DataObject
	 * If the name is not defined (by renaming $plural_name in the subclass),
	 * this returns a pluralised version of the class name.
	 *
	 * @return string User friendly plural name of this DataObject
	 */
	function plural_name() {
		if($name = $this->stat('plural_name')) {
			return $name;
		} else {
			$name = $this->singular_name();
			if(substr($name,-1) == 'e') $name = substr($name,0,-1);
			else if(substr($name,-1) == 'y') $name = substr($name,0,-1) . 'ie';

			return ucfirst($name . 's');
		}
	}

	/**
	 * Get the translated user friendly plural name of this DataObject
	 * Same as plural_name but runs it through the translation function
	 * Translation string is in the form:
	 *      $this->class.PLURALNAME
	 * Example:
	 *      Page.PLURALNAME
	 *
	 * @return string User friendly translated plural name of this DataObject
	 */
	function i18n_plural_name()
	{
		$name = $this->plural_name();
		return _t($this->class.'.PLURALNAME', $name);
	}
	
	/**
	 * Standard implementation of a title/label for a specific
	 * record. Tries to find properties 'Title' or 'Name',
	 * and falls back to the 'ID'. Useful to provide
	 * user-friendly identification of a record, e.g. in errormessages
	 * or UI-selections.
	 * 
	 * Overload this method to have a more specialized implementation,
	 * e.g. for an Address record this could be:
	 * <code>
	 * public function getTitle() {
	 *   return "{$this->StreetNumber} {$this->StreetName} {$this->City}";
	 * }
	 * </code>
	 *
	 * @return string
	 */
	public function getTitle() {
		if($this->hasDatabaseField('Title')) return $this->getField('Title');
		if($this->hasDatabaseField('Name')) return $this->getField('Name');
		
		return "#{$this->ID}";
	}

	/**
	 * Returns the associated database record - in this case, the object itself.
	 * This is included so that you can call $dataOrController->data() and get a DataObject all the time.
	 *
	 * @return DataObject Associated database record
	 */
	public function data() {
		return $this;
	}

	/**
	 * Convert this object to a map.
	 *
	 * @return array The data as a map.
	 */
	public function toMap() {
		return $this->record;
	}

	/**
	 * Update a number of fields on this object, given a map of the desired changes.
	 * 
	 * The field names can be simple names, or you can use a dot syntax to access $has_one relations.
	 * For example, array("Author.FirstName" => "Jim") will set $this->Author()->FirstName to "Jim".
	 * 
	 * update() doesn't write the main object, but if you use the dot syntax, it will write() 
	 * the related objects that it alters.
	 *
	 * @param array $data A map of field name to data values to update.
	 */
	public function update($data) {
		foreach($data as $k => $v) {
			// Implement dot syntax for updates
			if(strpos($k,'.') !== false) {
				$relations = explode('.', $k);
				$fieldName = array_pop($relations);
				$relObj = $this;
				foreach($relations as $i=>$relation) {
					// no support for has_many or many_many relationships,
					// as the updater wouldn't know which object to write to (or create)
					if($relObj->$relation() instanceof DataObject) {
						$relObj = $relObj->$relation();
						
						// If the intermediate relationship objects have been created, then write them
						if($i<sizeof($relation)-1 && !$relObj->ID) $relObj->write();
					} else {
						user_error(
							"DataObject::update(): Can't traverse relationship '$relation'," .  
							"it has to be a has_one relationship or return a single DataObject", 
							E_USER_NOTICE
						);
						// unset relation object so we don't write properties to the wrong object
						unset($relObj);
						break;
					}
				}

				if($relObj) {
					$relObj->$fieldName = $v;
					$relObj->write();
					$relObj->flushCache();
				} else {
					user_error("Couldn't follow dot syntax '$k' on '$this->class' object", E_USER_WARNING);
				}
			} else {
				$this->$k = $v;
			}
		}
	}
	
	/**
	 * Pass changes as a map, and try to
	 * get automatic casting for these fields.
	 * Doesn't write to the database. To write the data,
	 * use the write() method.
	 *
	 * @param array $data A map of field name to data values to update.
	 */
	public function castedUpdate($data) {
		foreach($data as $k => $v) {
			$this->setCastedField($k,$v);
		}
	}

	/**
	 * Merges data and relations from another object of same class,
	 * without conflict resolution. Allows to specify which
	 * dataset takes priority in case its not empty.
	 * has_one-relations are just transferred with priority 'right'.
	 * has_many and many_many-relations are added regardless of priority.
	 *
	 * Caution: has_many/many_many relations are moved rather than duplicated,
	 * meaning they are not connected to the merged object any longer.
	 * Caution: Just saves updated has_many/many_many relations to the database,
	 * doesn't write the updated object itself (just writes the object-properties).
	 * Caution: Does not delete the merged object.
	 * Caution: Does now overwrite Created date on the original object.
	 *
	 * @param $obj DataObject
	 * @param $priority String left|right Determines who wins in case of a conflict (optional)
	 * @param $includeRelations Boolean Merge any existing relations (optional)
	 * @param $overwriteWithEmpty Boolean Overwrite existing left values with empty right values.
	 * 	Only applicable with $priority='right'. (optional)
	 * @return Boolean
	 */
	public function merge($rightObj, $priority = 'right', $includeRelations = true, $overwriteWithEmpty = false) {
		$leftObj = $this;

		if($leftObj->ClassName != $rightObj->ClassName) {
			// we can't merge similiar subclasses because they might have additional relations
			user_error("DataObject->merge(): Invalid object class '{$rightObj->ClassName}'
			(expected '{$leftObj->ClassName}').", E_USER_WARNING);
			return false;
		}

		if(!$rightObj->ID) {
			user_error("DataObject->merge(): Please write your merged-in object to the database before merging,
				to make sure all relations are transferred properly.').", E_USER_WARNING);
			return false;
		}

		// makes sure we don't merge data like ID or ClassName
		$leftData = $leftObj->inheritedDatabaseFields();
		$rightData = $rightObj->inheritedDatabaseFields();

		foreach($rightData as $key=>$rightVal) {
			// don't merge conflicting values if priority is 'left'
			if($priority == 'left' && $leftObj->{$key} !== $rightObj->{$key}) continue;

			// don't overwrite existing left values with empty right values (if $overwriteWithEmpty is set)
			if($priority == 'right' && !$overwriteWithEmpty && empty($rightObj->{$key})) continue;

			// TODO remove redundant merge of has_one fields
			$leftObj->{$key} = $rightObj->{$key};
		}

		// merge relations
		if($includeRelations) {
			if($manyMany = $this->many_many()) {
				foreach($manyMany as $relationship => $class) {
					$leftComponents = $leftObj->getManyManyComponents($relationship);
					$rightComponents = $rightObj->getManyManyComponents($relationship);
					if($rightComponents && $rightComponents->exists()) $leftComponents->addMany($rightComponents->column('ID'));
					$leftComponents->write();
				}
			}

			if($hasMany = $this->has_many()) {
				foreach($hasMany as $relationship => $class) {
					$leftComponents = $leftObj->getComponents($relationship);
					$rightComponents = $rightObj->getComponents($relationship);
					if($rightComponents && $rightComponents->exists()) $leftComponents->addMany($rightComponents->column('ID'));
					$leftComponents->write();
				}

			}

			if($hasOne = $this->has_one()) {
				foreach($hasOne as $relationship => $class) {
					$leftComponent = $leftObj->getComponent($relationship);
					$rightComponent = $rightObj->getComponent($relationship);
					if($leftComponent->exists() && $rightComponent->exists() && $priority == 'right') {
						$leftObj->{$relationship . 'ID'} = $rightObj->{$relationship . 'ID'};
					}
				}
			}
		}

		return true;
	}

	/**
	 * Forces the record to think that all its data has changed.
	 * Doesn't write to the database. Only sets fields as changed
	 * if they are not already marked as changed.
	 */
	public function forceChange() {
		// $this->record might not contain the blank values so we loop on $this->inheritedDatabaseFields() as well
		$fieldNames = array_unique(array_merge(array_keys($this->record), array_keys($this->inheritedDatabaseFields())));
		
		foreach($fieldNames as $fieldName) {
			if(!isset($this->changed[$fieldName])) $this->changed[$fieldName] = 1;
			// Populate the null values in record so that they actually get written
			if(!isset($this->record[$fieldName])) $this->record[$fieldName] = null;
		}
		
		// @todo Find better way to allow versioned to write a new version after forceChange
		if($this->isChanged('Version')) unset($this->changed['Version']);
	}
	
	/**
	 * Validate the current object.
	 *
	 * By default, there is no validation - objects are always valid!  However, you can overload this method in your
	 * DataObject sub-classes to specify custom validation.
	 * 
	 * Invalid objects won't be able to be written - a warning will be thrown and no write will occur.  onBeforeWrite()
	 * and onAfterWrite() won't get called either.
	 * 
	 * It is expected that you call validate() in your own application to test that an object is valid before attempting
	 * a write, and respond appropriately if it isnt'.
	 * 
	 * @return A {@link ValidationResult} object
	 */
	protected function validate() {
		return new ValidationResult();
	}

	/**
	 * Event handler called before writing to the database.
	 * You can overload this to clean up or otherwise process data before writing it to the
	 * database.  Don't forget to call parent::onBeforeWrite(), though!
	 *
	 * This called after {@link $this->validate()}, so you can be sure that your data is valid.
	 * 
	 * @uses DataExtension->onBeforeWrite()
	 */
	protected function onBeforeWrite() {
		$this->brokenOnWrite = false;
		
		$dummy = null;
		$this->extend('onBeforeWrite', $dummy);
	}

	/**
	 * Event handler called after writing to the database.
	 * You can overload this to act upon changes made to the data after it is written.
	 * $this->changed will have a record
	 * database.  Don't forget to call parent::onAfterWrite(), though!
	 *
	 * @uses DataExtension->onAfterWrite()
	 */
	protected function onAfterWrite() {
		$dummy = null;
		$this->extend('onAfterWrite', $dummy);
	}

	/**
	 * Event handler called before deleting from the database.
	 * You can overload this to clean up or otherwise process data before delete this
	 * record.  Don't forget to call parent::onBeforeDelete(), though!
	 *
	 * @uses DataExtension->onBeforeDelete()
	 */
	protected function onBeforeDelete() {
		$this->brokenOnDelete = false;
		
		$dummy = null;
		$this->extend('onBeforeDelete', $dummy);
	}
	
	protected function onAfterDelete() {
		$this->extend('onAfterDelete');
	}

	/**
	 * Load the default values in from the self::$defaults array.
	 * Will traverse the defaults of the current class and all its parent classes.
	 * Called by the constructor when creating new records.
	 * 
	 *  @uses DataExtension->populateDefaults()
	 */
	public function populateDefaults() {
		$classes = array_reverse(ClassInfo::ancestry($this));
		
		foreach($classes as $class) {
			$defaults = Object::uninherited_static($class, 'defaults');
			
			if($defaults && !is_array($defaults)) {
				user_error("Bad '$this->class' defaults given: " . var_export($defaults, true),
				 	E_USER_WARNING);
				$defaults = null;
			}
			
			if($defaults) foreach($defaults as $fieldName => $fieldValue) {
				// SRM 2007-03-06: Stricter check
				if(!isset($this->$fieldName) || $this->$fieldName === null) {
					$this->$fieldName = $fieldValue;
				}
				// Set many-many defaults with an array of ids
				if(is_array($fieldValue) && $this->many_many($fieldName)) {
					$manyManyJoin = $this->$fieldName();
					$manyManyJoin->setByIdList($fieldValue);
				}
			}
			if($class == 'DataObject') {
				break;
			}
		}
		
		$this->extend('populateDefaults');
	}

	/**
	 * Writes all changes to this object to the database.
	 *  - It will insert a record whenever ID isn't set, otherwise update.
	 *  - All relevant tables will be updated.
	 *  - $this->onBeforeWrite() gets called beforehand.
	 *  - Extensions such as Versioned will ammend the database-write to ensure that a version is saved.
	 * 
	 *  @uses DataExtension->augmentWrite()
	 *
	 * @param boolean $showDebug Show debugging information
	 * @param boolean $forceInsert Run INSERT command rather than UPDATE, even if record already exists
	 * @param boolean $forceWrite Write to database even if there are no changes
	 * @param boolean $writeComponents Call write() on all associated component instances which were previously
	 * 					retrieved through {@link getComponent()}, {@link getComponents()} or {@link getManyManyComponents()}
	 * 					(Default: false)
	 *
	 * @return int The ID of the record
	 * @throws ValidationException Exception that can be caught and handled by the calling function
	 */
	public function write($showDebug = false, $forceInsert = false, $forceWrite = false, $writeComponents = false) {
		$firstWrite = false;
		$this->brokenOnWrite = true;
		$isNewRecord = false;
		
		if(self::get_validation_enabled()) {
			$valid = $this->validate();
			if(!$valid->valid()) {
				// Used by DODs to clean up after themselves, eg, Versioned
				$this->extend('onAfterSkippedWrite');
				throw new ValidationException($valid, "Validation error writing a $this->class object: " . $valid->message() . ".  Object not written.", E_USER_WARNING);
				return false;
			}
		}

		$this->onBeforeWrite();
		if($this->brokenOnWrite) {
			user_error("$this->class has a broken onBeforeWrite() function.  Make sure that you call parent::onBeforeWrite().", E_USER_ERROR);
		}

		// New record = everything has changed

		if(($this->ID && is_numeric($this->ID)) && !$forceInsert) {
			$dbCommand = 'update';

			// Update the changed array with references to changed obj-fields
			foreach($this->record as $k => $v) {
				if(is_object($v) && method_exists($v, 'isChanged') && $v->isChanged()) {
					$this->changed[$k] = true;
				}
			}

		} else{
			$dbCommand = 'insert';

			$this->changed = array();
			foreach($this->record as $k => $v) {
				$this->changed[$k] = 2;
			}
			
			$firstWrite = true;
		}

		// No changes made
		if($this->changed) {
			foreach($this->getClassAncestry() as $ancestor) {
				if(self::has_own_table($ancestor))
				$ancestry[] = $ancestor;
			}

			// Look for some changes to make
			if(!$forceInsert) unset($this->changed['ID']);

			$hasChanges = false;
			foreach($this->changed as $fieldName => $changed) {
				if($changed) {
					$hasChanges = true;
					break;
				}
			}

			if($hasChanges || $forceWrite || !$this->record['ID']) {
					
				// New records have their insert into the base data table done first, so that they can pass the
				// generated primary key on to the rest of the manipulation
				$baseTable = $ancestry[0];
				
				if((!isset($this->record['ID']) || !$this->record['ID']) && isset($ancestry[0])) {	

					DB::query("INSERT INTO \"{$baseTable}\" (\"Created\") VALUES (" . DB::getConn()->now() . ")");
					$this->record['ID'] = DB::getGeneratedID($baseTable);
					$this->changed['ID'] = 2;

					$isNewRecord = true;
				}

				// Divvy up field saving into a number of database manipulations
				$manipulation = array();
				if(isset($ancestry) && is_array($ancestry)) {
					foreach($ancestry as $idx => $class) {
						$classSingleton = singleton($class);
						
						foreach($this->record as $fieldName => $fieldValue) {
							if(isset($this->changed[$fieldName]) && $this->changed[$fieldName] && $fieldType = $classSingleton->hasOwnTableDatabaseField($fieldName)) {
								$fieldObj = $this->dbObject($fieldName);
								if(!isset($manipulation[$class])) $manipulation[$class] = array();

								// if database column doesn't correlate to a DBField instance...
								if(!$fieldObj) {
									$fieldObj = DBField::create('Varchar', $this->record[$fieldName], $fieldName);
								}

								// Both CompositeDBFields and regular fields need to be repopulated
								$fieldObj->setValue($this->record[$fieldName], $this->record);

								if($class != $baseTable || $fieldName!='ID')
									$fieldObj->writeToManipulation($manipulation[$class]);
							}
						}

						// Add the class name to the base object
						if($idx == 0) {
							$manipulation[$class]['fields']["LastEdited"] = "'".SS_Datetime::now()->Rfc2822()."'";
							if($dbCommand == 'insert') {
								$manipulation[$class]['fields']["Created"] = "'".SS_Datetime::now()->Rfc2822()."'";
								//echo "<li>$this->class - " .get_class($this);
								$manipulation[$class]['fields']["ClassName"] = "'$this->class'";
							}
						}

						// In cases where there are no fields, this 'stub' will get picked up on
						if(self::has_own_table($class)) {
							$manipulation[$class]['command'] = $dbCommand;
							$manipulation[$class]['id'] = $this->record['ID'];
						} else {
							unset($manipulation[$class]);
						}
					}
				}
				$this->extend('augmentWrite', $manipulation);
				
				// New records have their insert into the base data table done first, so that they can pass the
				// generated ID on to the rest of the manipulation
				if(isset($isNewRecord) && $isNewRecord && isset($manipulation[$baseTable])) {
					$manipulation[$baseTable]['command'] = 'update';
				}
				
				DB::manipulate($manipulation);
				$this->onAfterWrite();

				$this->changed = null;
			} elseif ( $showDebug ) {
				echo "<b>Debug:</b> no changes for DataObject<br />";
				// Used by DODs to clean up after themselves, eg, Versioned
				$this->extend('onAfterSkippedWrite');
			}

			// Clears the cache for this object so get_one returns the correct object.
			$this->flushCache();

			if(!isset($this->record['Created'])) {
				$this->record['Created'] = SS_Datetime::now()->Rfc2822();
			}
			$this->record['LastEdited'] = SS_Datetime::now()->Rfc2822();
		} else {
			// Used by DODs to clean up after themselves, eg, Versioned
			$this->extend('onAfterSkippedWrite');
		}

		// Write relations as necessary
		if($writeComponents) {
			$this->writeComponents(true);
		}
		return $this->record['ID'];
	}


	/**
	 * Write the cached components to the database. Cached components could refer to two different instances of the same record.
	 * 
	 * @param $recursive Recursively write components
	 */
	public function writeComponents($recursive = false) {
		if(!$this->components) return;
		
		foreach($this->components as $component) {
			$component->write(false, false, false, $recursive);
		}
	}
	
	/**
	 * Delete this data object.
	 * $this->onBeforeDelete() gets called.
	 * Note that in Versioned objects, both Stage and Live will be deleted.
	 *  @uses DataExtension->augmentSQL()
	 */
	public function delete() {
		$this->brokenOnDelete = true;
		$this->onBeforeDelete();
		if($this->brokenOnDelete) {
			user_error("$this->class has a broken onBeforeDelete() function.  Make sure that you call parent::onBeforeDelete().", E_USER_ERROR);
		}
		
        // Deleting a record without an ID shouldn't do anything
        if(!$this->ID) throw new Exception("DataObject::delete() called on a DataObject without an ID");

		// TODO: This is quite ugly.  To improve:
		//  - move the details of the delete code in the DataQuery system
		//  - update the code to just delete the base table, and rely on cascading deletes in the DB to do the rest
		//    obviously, that means getting requireTable() to configure cascading deletes ;-)
		$srcQuery = DataList::create($this->class, $this->model)->where("ID = $this->ID")->dataQuery()->query();
		foreach($srcQuery->queriedTables() as $table) {
			$query = new SQLQuery("*", array('"'.$table.'"'));
			$query->where("\"ID\" = $this->ID");
			$query->delete = true;
			$query->execute();
		}
		// Remove this item out of any caches
		$this->flushCache();
		
		$this->onAfterDelete();

		$this->OldID = $this->ID;
		$this->ID = 0;
	}

	/**
	 * Delete the record with the given ID.
	 *
	 * @param string $className The class name of the record to be deleted
	 * @param int $id ID of record to be deleted
	 */
	public static function delete_by_id($className, $id) {
		$obj = DataObject::get_by_id($className, $id);
		if($obj) {
			$obj->delete();
		} else {
			user_error("$className object #$id wasn't found when calling DataObject::delete_by_id", E_USER_WARNING);
		}
	}

	/**
	 * A cache used by getClassAncestry()
	 * @var array
	 */
	protected static $ancestry;

	/**
	 * Get the class ancestry, including the current class name.
	 * The ancestry will be returned as an array of class names, where the 0th element
	 * will be the class that inherits directly from DataObject, and the last element
	 * will be the current class.
	 *
	 * @return array Class ancestry
	 */
	public function getClassAncestry() {
		if(!isset(DataObject::$ancestry[$this->class])) {
			DataObject::$ancestry[$this->class] = array($this->class);
			while(($class = get_parent_class(DataObject::$ancestry[$this->class][0])) != "DataObject") {
				array_unshift(DataObject::$ancestry[$this->class], $class);
			}
		}
		return DataObject::$ancestry[$this->class];
	}

	/**
	 * Return a component object from a one to one relationship, as a DataObject.
	 * If no component is available, an 'empty component' will be returned.
	 *
	 * @param string $componentName Name of the component
	 *
	 * @return DataObject The component object. It's exact type will be that of the component.
	 */
	public function getComponent($componentName) {
		if(isset($this->components[$componentName])) {
			return $this->components[$componentName];
		}
		
		if($class = $this->has_one($componentName)) {
			$joinField = $componentName . 'ID';
			$joinID    = $this->getField($joinField);
			
			if($joinID) {
				$component = $this->model->$class->byID($joinID);
			}
			
			if(!isset($component) || !$component) {
				$component = $this->model->$class->newObject();
			}
		} elseif($class = $this->belongs_to($componentName)) {
			$joinField = $this->getRemoteJoinField($componentName, 'belongs_to');
			$joinID    = $this->ID;
			
			if($joinID) {
				$component = DataObject::get_one($class, "\"$joinField\" = $joinID");
			}
			
			if(!isset($component) || !$component) {
				$component = $this->model->$class->newObject();
				$component->$joinField = $this->ID;
			}
		} else {
			throw new Exception("DataObject->getComponent(): Could not find component '$componentName'.");
		}
		
		$this->components[$componentName] = $component;
		return $component;
	}

	/**
	 * A cache used by component getting classes
	 * @var array
	 */
	protected $componentCache;

	/**
	 * Returns a one-to-many relation as a HasManyList
	 *
	 * @param string $componentName Name of the component
	 * @param string $filter A filter to be inserted into the WHERE clause
	 * @param string|array $sort A sort expression to be inserted into the ORDER BY clause. If omitted, the static field $default_sort on the component class will be used.
	 * @param string $join A single join clause. This can be used for filtering, only 1 instance of each DataObject will be returned.
	 * @param string|array $limit A limit expression to be inserted into the LIMIT clause
	 *
	 * @return HasManyList The components of the one-to-many relationship.
	 */
	public function getComponents($componentName, $filter = "", $sort = "", $join = "", $limit = null) {
		$result = null;

		if(!$componentClass = $this->has_many($componentName)) {
			user_error("DataObject::getComponents(): Unknown 1-to-many component '$componentName' on class '$this->class'", E_USER_ERROR);
		}

		$joinField = $this->getRemoteJoinField($componentName, 'has_many');
		
		$result = new HasManyList($componentClass, $joinField);
		if($this->model) $result->setModel($this->model);
		$result->setForeignID($this->ID);

		$result = $result->where($filter)->limit($limit)->sort($sort);
		if($join) $result = $result->join($join);

		return $result;
	}

	/**
	 * Get the query object for a $has_many Component.
	 *
	 * @param string $componentName
	 * @param string $filter
	 * @param string|array $sort
	 * @param string $join
	 * @param string|array $limit
	 * @return SQLQuery
	 */
	public function getComponentsQuery($componentName, $filter = "", $sort = "", $join = "", $limit = "") {
		if(!$componentClass = $this->has_many($componentName)) {
			user_error("DataObject::getComponentsQuery(): Unknown 1-to-many component '$componentName' on class '$this->class'", E_USER_ERROR);
		}

		$joinField = $this->getRemoteJoinField($componentName, 'has_many');

		$id = $this->getField("ID");
			
		// get filter
		$combinedFilter = "\"$joinField\" = '$id'";
		if($filter) $combinedFilter .= " AND {$filter}";
			
		return singleton($componentClass)->extendedSQL($combinedFilter, $sort, $limit, $join);
	}
	
	/**
	 * Tries to find the database key on another object that is used to store a relationship to this class. If no join
	 * field can be found it defaults to 'ParentID'.
	 *
	 * @param string $component
	 * @param string $type the join type - either 'has_many' or 'belongs_to'
	 * @return string
	 */
	public function getRemoteJoinField($component, $type = 'has_many') {
		$remoteClass = $this->$type($component, false);
		
		if(!$remoteClass) {
			throw new Exception("Unknown $type component '$component' on class '$this->class'");
		}
		
		if($fieldPos = strpos($remoteClass, '.')) {
			return substr($remoteClass, $fieldPos + 1) . 'ID';
		}
		
		$remoteRelations = array_flip(Object::combined_static($remoteClass, 'has_one', 'DataObject'));
		
		// look for remote has_one joins on this class or any parent classes
		foreach(array_reverse(ClassInfo::ancestry($this)) as $class) {
			if(array_key_exists($class, $remoteRelations)) return $remoteRelations[$class] . 'ID';
		}
		
		return 'ParentID';
	}
	
	/**
	 * Sets the component of a relationship.
	 * This should only need to be called internally,
	 * and is mainly due to the caching logic in {@link getComponents()}
	 * and {@link getManyManyComponents()}.
	 *
	 * @param string $componentName Name of the component
	 * @param DataObject|HasManyList|ManyManyList $componentValue Value of the component
	 */
	public function setComponent($componentName, $componentValue) {
		$this->componentCache[$componentName] = $componentValue;
	}

	/**
	 * Returns a many-to-many component, as a ManyManyList.
	 * @param string $componentName Name of the many-many component
	 * @return ManyManyList The set of components
	 *
	 * @todo Implement query-params
	 */
	public function getManyManyComponents($componentName, $filter = "", $sort = "", $join = "", $limit = "") {
		list($parentClass, $componentClass, $parentField, $componentField, $table) = $this->many_many($componentName);
		
		$result = new ManyManyList($componentClass, $table, $componentField, $parentField,
			$this->many_many_extraFields($componentName));
		if($this->model) $result->setModel($this->model);

		// If this is called on a singleton, then we return an 'orphaned relation' that can have the
		// foreignID set elsewhere.
		$result->setForeignID($this->ID);
			
		return $result->where($filter)->sort($sort)->limit($limit);
	}
	
	/**
	 * Return the class of a one-to-one component.  If $component is null, return all of the one-to-one components and their classes.
	 *
	 * @param string $component Name of component
	 *
	 * @return string|array The class of the one-to-one component, or an array of all one-to-one components and their classes.
	 */
	public function has_one($component = null) {
		$classes = ClassInfo::ancestry($this);

		foreach($classes as $class) {
			// Wait until after we reach DataObject
			if(in_array($class, array('Object', 'ViewableData', 'DataObject'))) continue;

			if($component) {
				$hasOne = Object::uninherited_static($class, 'has_one');
				
				if(isset($hasOne[$component])) {
					return $hasOne[$component];
				}
			} else {
				$newItems = (array) Object::uninherited_static($class, 'has_one');
				// Validate the data
				foreach($newItems as $k => $v) {
					if(!is_string($k) || is_numeric($k) || !is_string($v)) user_error("$class::\$has_one has a bad entry: " 
						. var_export($k,true). " => " . var_export($v,true) . ".  Each map key should be a relationship name, and the map value should be the data class to join to.", E_USER_ERROR);
				}
				$items = isset($items) ? array_merge($newItems, (array)$items) : $newItems;
			}
		}
		return isset($items) ? $items : null;
	}
	
	/**
	 * Returns the class of a remote belongs_to relationship. If no component is specified a map of all components and
	 * their class name will be returned.
	 *
	 * @param string $component
	 * @param bool $classOnly If this is TRUE, than any has_many relationships in the form "ClassName.Field" will have
	 *        the field data stripped off. It defaults to TRUE.
	 * @return string|array
	 */
	public function belongs_to($component = null, $classOnly = true) {
		$belongsTo = Object::combined_static($this->class, 'belongs_to', 'DataObject');
		
		if($component) {
			if($belongsTo && array_key_exists($component, $belongsTo)) {
				$belongsTo = $belongsTo[$component];
			} else {
				return false;
			}
		}
		
		if($belongsTo && $classOnly) {
			return preg_replace('/(.+)?\..+/', '$1', $belongsTo);
		} else {
			return $belongsTo ? $belongsTo : array();
		}
	}
	
	/**
	 * Return all of the database fields defined in self::$db and all the parent classes.
	 * Doesn't include any fields specified by self::$has_one.  Use $this->has_one() to get these fields
	 *
	 * @param string $fieldName Limit the output to a specific field name
	 * @return array The database fields
	 */
	public function db($fieldName = null) {
		$classes = ClassInfo::ancestry($this);
		$good = false;
		$items = array();
		
		foreach($classes as $class) {
			// Wait until after we reach DataObject
			if(!$good) {
				if($class == 'DataObject') {
					$good = true;
				}
				continue;
			}

			if($fieldName) {
				$db = Object::uninherited_static($class, 'db');
				
				if(isset($db[$fieldName])) {
					return $db[$fieldName];
				}
			} else {
				$newItems = (array) Object::uninherited_static($class, 'db');
				// Validate the data
				foreach($newItems as $k => $v) {
					if(!is_string($k) || is_numeric($k) || !is_string($v)) user_error("$class::\$db has a bad entry: " 
						. var_export($k,true). " => " . var_export($v,true) . ".  Each map key should be a property name, and the map value should be the property type.", E_USER_ERROR);
				}
				$items = isset($items) ? array_merge((array)$items, $newItems) : $newItems;
			}
		}

		return $items;
	}

	/**
	 * Gets the class of a one-to-many relationship. If no $component is specified then an array of all the one-to-many
	 * relationships and their classes will be returned.
	 *
	 * @param string $component Name of component
	 * @param bool $classOnly If this is TRUE, than any has_many relationships in the form "ClassName.Field" will have
	 *        the field data stripped off. It defaults to TRUE.
	 * @return string|array
	 */
	public function has_many($component = null, $classOnly = true) {
		$hasMany = Object::combined_static($this->class, 'has_many', 'DataObject');
		
		if($component) {
			if($hasMany && array_key_exists($component, $hasMany)) {
				$hasMany = $hasMany[$component];
			} else {
				return false;
			}
		}
		
		if($hasMany && $classOnly) {
			return preg_replace('/(.+)?\..+/', '$1', $hasMany);
		} else {
			return $hasMany ? $hasMany : array();
		}
	}

	/**
	 * Return the many-to-many extra fields specification.
	 * 
	 * If you don't specify a component name, it returns all
	 * extra fields for all components available.
	 * 
	 * @param string $component Name of component
	 * @return array
	 */
	public function many_many_extraFields($component = null) {
		$classes = ClassInfo::ancestry($this);

		foreach($classes as $class) {
			if(in_array($class, array('ViewableData', 'Object', 'DataObject'))) continue;
			$relationName = null;

			// Find extra fields for one component
			if($component) {
				$SNG_class = singleton($class);
				$extraFields = $SNG_class->stat('many_many_extraFields');

				// Extra fields are immediately available on this class
				if(isset($extraFields[$component])) {
					return $extraFields[$component];
				}
				
				$manyMany = $SNG_class->stat('many_many');
				$candidate = (isset($manyMany[$component])) ? $manyMany[$component] : null;
				if($candidate) {
					$SNG_candidate = singleton($candidate);
					$candidateManyMany = $SNG_candidate->stat('belongs_many_many');
					
					// Find the relation given the class
					if($candidateManyMany) foreach($candidateManyMany as $relation => $relatedClass) {
						if($relatedClass == $class) {
							$relationName = $relation;
							break;
						}
					}
					
					if($relationName) {
						$extraFields = $SNG_candidate->stat('many_many_extraFields');
						if(isset($extraFields[$relationName])) {
							return $extraFields[$relationName];
						}
					}
				}
								
				$manyMany = $SNG_class->stat('belongs_many_many');
				$candidate = (isset($manyMany[$component])) ? $manyMany[$component] : null;
				if($candidate) {
					$SNG_candidate = singleton($candidate);
					$candidateManyMany = $SNG_candidate->stat('many_many');
					
					// Find the relation given the class
					if($candidateManyMany) foreach($candidateManyMany as $relation => $relatedClass) {
						if($relatedClass == $class) {
							$relationName = $relation;
						}
					}
					
					$extraFields = $SNG_candidate->stat('many_many_extraFields');
					if(isset($extraFields[$relationName])) {
						return $extraFields[$relationName];
					}
				}
				
			} else {
				
				// Find all the extra fields for all components
				$newItems = eval("return (array){$class}::\$many_many_extraFields;");
				
				foreach($newItems as $k => $v) {
					if(!is_array($v)) {
						user_error(
							"$class::\$many_many_extraFields has a bad entry: "
							. var_export($k, true) . " => " . var_export($v, true)
							. ". Each many_many_extraFields entry should map to a field specification array.",
							E_USER_ERROR
						);
					}
				}
					
				return isset($items) ? array_merge($newItems, $items) : $newItems;
			}
		}
	}
	
	/**
	 * Return information about a many-to-many component.
	 * The return value is an array of (parentclass, childclass).  If $component is null, then all many-many
	 * components are returned.
	 *
	 * @param string $component Name of component
	 *
	 * @return array  An array of (parentclass, childclass), or an array of all many-many components
	 */
	public function many_many($component = null) {
		$classes = ClassInfo::ancestry($this);

		foreach($classes as $class) {
			// Wait until after we reach DataObject
			if(in_array($class, array('ViewableData', 'Object', 'DataObject'))) continue;

			if($component) {
				$manyMany = Object::uninherited_static($class, 'many_many');
				// Try many_many
				$candidate = (isset($manyMany[$component])) ? $manyMany[$component] : null;
				if($candidate) {
					$parentField = $class . "ID";
					$childField = ($class == $candidate) ? "ChildID" : $candidate . "ID";
					return array($class, $candidate, $parentField, $childField, "{$class}_$component");
				}

				// Try belongs_many_many
				$belongsManyMany = Object::uninherited_static($class, 'belongs_many_many');
				$candidate = (isset($belongsManyMany[$component])) ? $belongsManyMany[$component] : null;
				if($candidate) {
					$childField = $candidate . "ID";

					// We need to find the inverse component name
					$otherManyMany = Object::uninherited_static($candidate, 'many_many');
					if(!$otherManyMany) {
						user_error("Inverse component of $candidate not found ({$this->class})", E_USER_ERROR);
					}

					foreach($otherManyMany as $inverseComponentName => $candidateClass) {
						if($candidateClass == $class || is_subclass_of($class, $candidateClass)) {
							$parentField = ($class == $candidate) ? "ChildID" : $candidateClass . "ID";
							// HACK HACK HACK!
							if($component == 'NestedProducts') {
								$parentField = $candidateClass . "ID";
							}

							return array($class, $candidate, $parentField, $childField, "{$candidate}_$inverseComponentName");
						}
					}
					user_error("Orphaned \$belongs_many_many value for $this->class.$component", E_USER_ERROR);
				}
			} else {
				$newItems = (array) Object::uninherited_static($class, 'many_many');
				// Validate the data
				foreach($newItems as $k => $v) {
					if(!is_string($k) || is_numeric($k) || !is_string($v)) user_error("$class::\$many_many has a bad entry: " 
						. var_export($k,true). " => " . var_export($v,true) . ".  Each map key should be a relationship name, and the map value should be the data class to join to.", E_USER_ERROR);
				}
				$items = isset($items) ? array_merge($newItems, $items) : $newItems;
				
				$newItems = (array) Object::uninherited_static($class, 'belongs_many_many');
				// Validate the data
				foreach($newItems as $k => $v) {
					if(!is_string($k) || is_numeric($k) || !is_string($v)) user_error("$class::\$belongs_many_many has a bad entry: " 
						. var_export($k,true). " => " . var_export($v,true) . ".  Each map key should be a relationship name, and the map value should be the data class to join to.", E_USER_ERROR);
				}

				$items = isset($items) ? array_merge($newItems, $items) : $newItems;
			}
		}
		
		return isset($items) ? $items : null;
	}
	
	/**
	 * This returns an array (if it exists) describing the database extensions that are required, or false if none
	 * 
	 * This is experimental, and is currently only a Postgres-specific enhancement.
	 * 
	 * @return array or false
	 */
	function database_extensions($class){
		
		$extensions = Object::uninherited_static($class, 'database_extensions');
		
		if($extensions)
			return $extensions;
		else
			return false;
	}

	/**
	 * Generates a SearchContext to be used for building and processing
	 * a generic search form for properties on this object.
	 *
	 * @return SearchContext
	 */
	public function getDefaultSearchContext() {
		return new SearchContext(
			$this->class, 
			$this->scaffoldSearchFields(), 
			$this->defaultSearchFilters()
		);
	}
	
	/**
	 * Determine which properties on the DataObject are
	 * searchable, and map them to their default {@link FormField}
	 * representations. Used for scaffolding a searchform for {@link ModelAdmin}.
	 *
	 * Some additional logic is included for switching field labels, based on
	 * how generic or specific the field type is.
	 *
	 * Used by {@link SearchContext}.
	 * 
	 * @param array $_params
	 * 	'fieldClasses': Associative array of field names as keys and FormField classes as values
	 * 	'restrictFields': Numeric array of a field name whitelist
	 * @return FieldList
	 */
	public function scaffoldSearchFields($_params = null) {
		$params = array_merge(
			array(
				'fieldClasses' => false,
				'restrictFields' => false
			),
			(array)$_params
		);
		$fields = new FieldList();
		foreach($this->searchableFields() as $fieldName => $spec) {
			if($params['restrictFields'] && !in_array($fieldName, $params['restrictFields'])) continue;
			
			// If a custom fieldclass is provided as a string, use it
			if($params['fieldClasses'] && isset($params['fieldClasses'][$fieldName])) {
				$fieldClass = $params['fieldClasses'][$fieldName];
				$field = new $fieldClass($fieldName);
			// If we explicitly set a field, then construct that
			} else if(isset($spec['field'])) {
				// If it's a string, use it as a class name and construct
				if(is_string($spec['field'])) {
					$fieldClass = $spec['field'];
					$field = new $fieldClass($fieldName);
					
				// If it's a FormField object, then just use that object directly.
				} else if($spec['field'] instanceof FormField) {
					$field = $spec['field'];
					
				// Otherwise we have a bug
				} else {
					user_error("Bad value for searchable_fields, 'field' value: " . var_export($spec['field'], true), E_USER_WARNING);
				}
				
			// Otherwise, use the database field's scaffolder
			} else {
				$field = $this->relObject($fieldName)->scaffoldSearchField();
			}

			if (strstr($fieldName, '.')) {
				$field->setName(str_replace('.', '__', $fieldName));
			}
			$field->setTitle($spec['title']);

			$fields->push($field);
		}
		return $fields;
	}

	/**
	 * Scaffold a simple edit form for all properties on this dataobject,
	 * based on default {@link FormField} mapping in {@link DBField::scaffoldFormField()}.
	 * Field labels/titles will be auto generated from {@link DataObject::fieldLabels()}.
	 *
	 * @uses FormScaffolder
	 * 
	 * @param array $_params Associative array passing through properties to {@link FormScaffolder}.
	 * @return FieldList
	 */
	public function scaffoldFormFields($_params = null) {
		$params = array_merge(
			array(
				'tabbed' => false,
				'includeRelations' => false,
				'restrictFields' => false,
				'fieldClasses' => false,
				'ajaxSafe' => false
			),
			(array)$_params
		);
		
		$fs = new FormScaffolder($this);
		$fs->tabbed = $params['tabbed'];
		$fs->includeRelations = $params['includeRelations'];
		$fs->restrictFields = $params['restrictFields'];
		$fs->fieldClasses = $params['fieldClasses'];
		$fs->ajaxSafe = $params['ajaxSafe'];
		
		return $fs->getFieldSet();
	}
	
	/**
	 * Centerpiece of every data administration interface in Silverstripe,
	 * which returns a {@link FieldList} suitable for a {@link Form} object.
	 * If not overloaded, we're using {@link scaffoldFormFields()} to automatically
	 * generate this set. To customize, overload this method in a subclass
	 * or extended onto it by using {@link DataExtension->updateCMSFields()}.
	 *
	 * <code>
	 * klass MyCustomClass extends DataObject {
	 * 	static $db = array('CustomProperty'=>'Boolean');
	 *
	 * 	public function getCMSFields() {
	 * 		$fields = parent::getCMSFields();
	 * 		$fields->addFieldToTab('Root.Content',new CheckboxField('CustomProperty'));
	 *		return $fields;
	 *	}
	 * }
	 * </code>
	 *
	 * @see Good example of complex FormField building: SiteTree::getCMSFields()
	 *
	 * @param array $params See {@link scaffoldFormFields()}
	 * @return FieldList Returns a TabSet for usage within the CMS - don't use for frontend forms.
	 */
	public function getCMSFields($params = null) {
		$tabbedFields = $this->scaffoldFormFields(array_merge(
			array(
				'includeRelations' => true,
				'tabbed' => true,
				'ajaxSafe' => true
			),
			(array)$params
		));
		
		$this->extend('updateCMSFields', $tabbedFields);
		
		return $tabbedFields;
	}
	
	/**
	 * need to be overload by solid dataobject, so that the customised actions of that dataobject,
	 * including that dataobject's extensions customised actions could be added to the EditForm.
	 * 
	 * @return an Empty FieldList(); need to be overload by solid subclass
	 */
	public function getCMSActions() {
		$actions = new FieldList();
		$this->extend('updateCMSActions', $actions);
		return $actions;
	}
	

	/**
	 * Used for simple frontend forms without relation editing
	 * or {@link TabSet} behaviour. Uses {@link scaffoldFormFields()}
	 * by default. To customize, either overload this method in your
	 * subclass, or extend it by {@link DataExtension->updateFrontEndFields()}.
	 * 
	 * @todo Decide on naming for "website|frontend|site|page" and stick with it in the API
	 *
	 * @param array $params See {@link scaffoldFormFields()}
	 * @return FieldList Always returns a simple field collection without TabSet.
	 */
	public function getFrontEndFields($params = null) {
		$untabbedFields = $this->scaffoldFormFields($params);
		$this->extend('updateFrontEndFields', $untabbedFields);
	
		return $untabbedFields;
	}

	/**
	 * Gets the value of a field.
	 * Called by {@link __get()} and any getFieldName() methods you might create.
	 *
	 * @param string $field The name of the field
	 *
	 * @return mixed The field value
	 */
	public function getField($field) {
		// If we already have an object in $this->record, then we should just return that
		if(isset($this->record[$field]) && is_object($this->record[$field]))  return $this->record[$field];
		
		// Otherwise, we need to determine if this is a complex field
		if(self::is_composite_field($this->class, $field)) {
			$helper = $this->castingHelper($field);
			$fieldObj = Object::create_from_string($helper, $field);
			
			// write value only if either the field value exists,
			// or a valid record has been loaded from the database
			$value = (isset($this->record[$field])) ? $this->record[$field] : null;
			if($value || $this->exists()) $fieldObj->setValue($value, $this->record, false);
			
			$this->record[$field] = $fieldObj;

			return $this->record[$field];
		}

		return isset($this->record[$field]) ? $this->record[$field] : null;
	}

	/**
	 * Return a map of all the fields for this record.
	 *
	 * @return array A map of field names to field values.
	 */
	public function getAllFields() {
		return $this->record;
	}

	/**
	 * Return the fields that have changed.
	 * 
	 * The change level affects what the functions defines as "changed":
	 * - Level 1 will return strict changes, even !== ones.
	 * - Level 2 is more lenient, it will only return real data changes, for example a change from 0 to null
	 * would not be included.
	 *
	 * Example return:
	 * <code>
	 * array(
	 *   'Title' = array('before' => 'Home', 'after' => 'Home-Changed', 'level' => 2)
	 * )
	 * </code>
	 *
	 * @param boolean $databaseFieldsOnly Get only database fields that have changed
	 * @param int $changeLevel The strictness of what is defined as change
	 * @return array
	 */
	public function getChangedFields($databaseFieldsOnly = false, $changeLevel = 1) {
		$changedFields = array();
		
		// Update the changed array with references to changed obj-fields
		foreach($this->record as $k => $v) {
			if(is_object($v) && method_exists($v, 'isChanged') && $v->isChanged()) {
				$this->changed[$k] = 2;
			}
		}
		
		if($databaseFieldsOnly) {
			$databaseFields = $this->inheritedDatabaseFields();
			$databaseFields['ID'] = true;
			$databaseFields['LastEdited'] = true;
			$databaseFields['Created'] = true;
			$databaseFields['ClassName'] = true;
			$fields = array_intersect_key((array)$this->changed, $databaseFields);
		} else {
			$fields = $this->changed;
		}

		// Filter the list to those of a certain change level
		if($changeLevel > 1) {
			if($fields) foreach($fields as $name => $level) {
				if($level < $changeLevel) {
					unset($fields[$name]);
				}
			}
		}
		
		if($fields) foreach($fields as $name => $level) {
			$changedFields[$name] = array(
				'before' => array_key_exists($name, $this->original) ? $this->original[$name] : null,
				'after' => array_key_exists($name, $this->record) ? $this->record[$name] : null,
				'level' => $level
			);
		}

		return $changedFields;
	}
	
	/**
	 * Uses {@link getChangedFields()} to determine if fields have been changed
	 * since loading them from the database.
	 * 
	 * @param string $fieldName Name of the database field to check, will check for any if not given
	 * @param int $changeLevel See {@link getChangedFields()}
	 * @return boolean
	 */
	function isChanged($fieldName = null, $changeLevel = 1) {
		$changed = $this->getChangedFields(false, $changeLevel);
		if(!isset($fieldName)) {
			return !empty($changed);
		} 
		else {
			return array_key_exists($fieldName, $changed);
		}
	}

	/**
	 * Set the value of the field
	 * Called by {@link __set()} and any setFieldName() methods you might create.
	 *
	 * @param string $fieldName Name of the field
	 * @param mixed $val New field value
	 */
	function setField($fieldName, $val) {
		// Situation 1: Passing an DBField
		if($val instanceof DBField) {
			$val->Name = $fieldName;
			$this->record[$fieldName] = $val;
		// Situation 2: Passing a literal or non-DBField object
		} else {
			// If this is a proper database field, we shouldn't be getting non-DBField objects
			if(is_object($val) && $this->db($fieldName)) {
				user_error('DataObject::setField: passed an object that is not a DBField', E_USER_WARNING);
			}
		
			$defaults = $this->stat('defaults');
			// if a field is not existing or has strictly changed
			if(!isset($this->record[$fieldName]) || $this->record[$fieldName] !== $val) {
				// TODO Add check for php-level defaults which are not set in the db
				// TODO Add check for hidden input-fields (readonly) which are not set in the db
				// At the very least, the type has changed
				$this->changed[$fieldName] = 1;
				
				if((!isset($this->record[$fieldName]) && $val) || (isset($this->record[$fieldName]) && $this->record[$fieldName] != $val)) {
					// Value has changed as well, not just the type
					$this->changed[$fieldName] = 2;
				}

				// value is always saved back when strict check succeeds
				$this->record[$fieldName] = $val;
			}
		}
	}

	/**
	 * Set the value of the field, using a casting object.
	 * This is useful when you aren't sure that a date is in SQL format, for example.
	 * setCastedField() can also be used, by forms, to set related data.  For example, uploaded images
	 * can be saved into the Image table.
	 *
	 * @param string $fieldName Name of the field
	 * @param mixed $value New field value
	 */
	public function setCastedField($fieldName, $val) {
		if(!$fieldName) {
			user_error("DataObject::setCastedField: Called without a fieldName", E_USER_ERROR);
		}
		$castingHelper = $this->castingHelper($fieldName);
		if($castingHelper) {
			$fieldObj = Object::create_from_string($castingHelper, $fieldName);
			$fieldObj->setValue($val);
			$fieldObj->saveInto($this);
		} else {
			$this->$fieldName = $val;
		}
	}

	/**
	 * Returns true if the given field exists
	 * in a database column on any of the objects tables,
	 * or as a dynamic getter with get<fieldName>().
	 *
	 * @param string $field Name of the field
	 * @return boolean True if the given field exists
	 */
	public function hasField($field) {
		return (
			array_key_exists($field, $this->record) 
			|| $this->db($field)
			|| $this->hasMethod("get{$field}")
		);
	}

	/**
	 * Returns true if the given field exists as a database column
	 *
	 * @param string $field Name of the field
	 *
	 * @return boolean
	 */
	public function hasDatabaseField($field) {
		// Add base fields which are not defined in static $db
		static $fixedFields = array(
			'ID' => 'Int',
			'ClassName' => 'Enum',
			'LastEdited' => 'SS_Datetime',
			'Created' => 'SS_Datetime',
		);
		
		if(isset($fixedFields[$field])) return true;

		return array_key_exists($field, $this->inheritedDatabaseFields());
	}
	
	/**
	 * Returns the field type of the given field, if it belongs to this class, and not a parent.
	 * Note that the field type will not include constructor arguments in round brackets, only the classname.
	 *
	 * @param string $field Name of the field
	 * @return string The field type of the given field
	 */
	public function hasOwnTableDatabaseField($field) {
		// Add base fields which are not defined in static $db
		if($field == "ID") return "Int";
		if($field == "ClassName" && get_parent_class($this) == "DataObject") return "Enum";
		if($field == "LastEdited" && get_parent_class($this) == "DataObject") return "SS_Datetime";
		if($field == "Created" && get_parent_class($this) == "DataObject") return "SS_Datetime";

		// Add fields from Versioned extension
		if($field == 'Version' && $this->hasExtension('Versioned')) { 
			return 'Int';
		}
		// get cached fieldmap
		$fieldMap = isset(self::$cache_has_own_table_field[$this->class]) ? self::$cache_has_own_table_field[$this->class] : null;
		
		// if no fieldmap is cached, get all fields
		if(!$fieldMap) {
			$fieldMap = Object::uninherited_static($this->class, 'db');
			
			// all $db fields on this specific class (no parents)
			foreach(self::composite_fields($this->class, false) as $fieldname => $fieldtype) {
				$combined_db = singleton($fieldtype)->compositeDatabaseFields();
				foreach($combined_db as $name => $type){
					$fieldMap[$fieldname.$name] = $type;
				}
			}
			
			// all has_one relations on this specific class,
			// add foreign key
			$hasOne = Object::uninherited_static($this->class, 'has_one');
			if($hasOne) foreach($hasOne as $fieldName => $fieldSchema) {
				$fieldMap[$fieldName . 'ID'] = "ForeignKey";
			}

			// set cached fieldmap
			self::$cache_has_own_table_field[$this->class] = $fieldMap;
		}

		// Remove string-based "constructor-arguments" from the DBField definition
		if(isset($fieldMap[$field])) {
			if(is_string($fieldMap[$field])) return strtok($fieldMap[$field],'(');
			else return $fieldMap[$field]['type'];
		}
	}
	
	/**
	 * Returns true if given class has its own table. Uses the rules for whether the table should exist rather than
	 * actually looking in the database.
	 *
	 * @param string $dataClass
	 * @return bool
	 */
	public static function has_own_table($dataClass) {
		
		// The condition below has the same effect as !is_subclass_of($dataClass,'DataObject'),
		// which causes PHP < 5.3 to segfault in rare circumstances, see PHP bug #46753
		if($dataClass == 'DataObject' || !in_array('DataObject', ClassInfo::ancestry($dataClass))) return false;
		
		if(!isset(self::$cache_has_own_table[$dataClass])) {
			if(get_parent_class($dataClass) == 'DataObject') {
				self::$cache_has_own_table[$dataClass] = true;
			} else {
				self::$cache_has_own_table[$dataClass] = Object::uninherited_static($dataClass, 'db') || Object::uninherited_static($dataClass, 'has_one');
			}
		}
		return self::$cache_has_own_table[$dataClass];
	}
	
	/**
	 * Returns true if the member is allowed to do the given action.
	 * See {@link extendedCan()} for a more versatile tri-state permission control.
	 *
	 * @param string $perm The permission to be checked, such as 'View'.
	 * @param Member $member The member whose permissions need checking.  Defaults to the currently logged
	 * in user.
	 *
	 * @return boolean True if the the member is allowed to do the given action
	 */
	function can($perm, $member = null) {
		if(!isset($member)) {
			$member = Member::currentUser();
		}
		if(Permission::checkMember($member, "ADMIN")) return true;

		if($this->many_many('Can' . $perm)) {
			if($this->ParentID && $this->SecurityType == 'Inherit') {
				if(!($p = $this->Parent)) {
					return false;
				}
				return $this->Parent->can($perm, $member);

			} else {
				$permissionCache = $this->uninherited('permissionCache');
				$memberID = $member ? $member->ID : 'none';

				if(!isset($permissionCache[$memberID][$perm])) {
					if($member->ID) {
						$groups = $member->Groups();
					}

					$groupList = implode(', ', $groups->column("ID"));

					// TODO Fix relation table hardcoding
					$query = new SQLQuery(
						"\"Page_Can$perm\".PageID",
					array("\"Page_Can$perm\""),
						"GroupID IN ($groupList)");

					$permissionCache[$memberID][$perm] = $query->execute()->column();

					if($perm == "View") {
						// TODO Fix relation table hardcoding
						$query = new SQLQuery("\"SiteTree\".\"ID\"", array(
							"\"SiteTree\"",
							"LEFT JOIN \"Page_CanView\" ON \"Page_CanView\".\"PageID\" = \"SiteTree\".\"ID\""
							), "\"Page_CanView\".\"PageID\" IS NULL");

							$unsecuredPages = $query->execute()->column();
							if($permissionCache[$memberID][$perm]) {
								$permissionCache[$memberID][$perm] = array_merge($permissionCache[$memberID][$perm], $unsecuredPages);
							} else {
								$permissionCache[$memberID][$perm] = $unsecuredPages;
							}
					}

					$this->set_uninherited('permissionCache', $permissionCache);
				}


				if($permissionCache[$memberID][$perm]) {
					return in_array($this->ID, $permissionCache[$memberID][$perm]);
				}
			}
		} else {
			return parent::can($perm, $member);
		}
	}

	/**
	 * Process tri-state responses from permission-alterting extensions.  The extensions are
	 * expected to return one of three values:
	 * 
	 *  - false: Disallow this permission, regardless of what other extensions say
	 *  - true: Allow this permission, as long as no other extensions return false
	 *  - NULL: Don't affect the outcome
	 * 
	 * This method itself returns a tri-state value, and is designed to be used like this:
	 *
	 * <code>
	 * $extended = $this->extendedCan('canDoSomething', $member);
	 * if($extended !== null) return $extended;
	 * else return $normalValue;
	 * </code>
	 * 
	 * @param String $methodName Method on the same object, e.g. {@link canEdit()}
	 * @param Member|int $member
	 * @return boolean|null
	 */
	public function extendedCan($methodName, $member) {
		$results = $this->extend($methodName, $member);
		if($results && is_array($results)) {
			// Remove NULLs
			$results = array_filter($results, array($this,'isNotNull'));
			// If there are any non-NULL responses, then return the lowest one of them.
			// If any explicitly deny the permission, then we don't get access 
			if($results) return min($results);
		}
		return null;
	}
	
	/**
	 * Helper functon for extendedCan
	 * 
	 * @param Mixed $value
	 * @return boolean
	 */
	private function isNotNull($value) {
		return !is_null($value);
	}

	/**
	 * @param Member $member
	 * @return boolean
	 */
	public function canView($member = null) {
		return Permission::check('ADMIN', 'any', $member);
	}

	/**
	 * @param Member $member
	 * @return boolean
	 */
	public function canEdit($member = null) {
		return Permission::check('ADMIN', 'any', $member);
	}

	/**
	 * @param Member $member
	 * @return boolean
	 */
	public function canDelete($member = null) {
		return Permission::check('ADMIN', 'any', $member);
	}

	/**
	 * @todo Should canCreate be a static method?
	 *
	 * @param Member $member
	 * @return boolean
	 */
	public function canCreate($member = null) {
		return Permission::check('ADMIN', 'any', $member);
	}

	/**
	 * Debugging used by Debug::show()
	 *
	 * @return string HTML data representing this object
	 */
	public function debug() {
		$val = "<h3>Database record: $this->class</h3>\n<ul>\n";
		if($this->record) foreach($this->record as $fieldName => $fieldVal) {
			$val .= "\t<li>$fieldName: " . Debug::text($fieldVal) . "</li>\n";
		}
		$val .= "</ul>\n";
		return $val;
	}

	/**
	 * Return the DBField object that represents the given field.
	 * This works similarly to obj() with 2 key differences:
	 *   - it still returns an object even when the field has no value.
	 *   - it only matches fields and not methods
	 *   - it matches foreign keys generated by has_one relationships, eg, "ParentID"
	 *
	 * @param string $fieldName Name of the field
	 * @return DBField The field as a DBField object
	 */
	public function dbObject($fieldName) {
		// If we have a CompositeDBField object in $this->record, then return that
		if(isset($this->record[$fieldName]) && is_object($this->record[$fieldName])) {
			return $this->record[$fieldName];
			
		// Special case for ID field
		} else if($fieldName == 'ID') {
			return new PrimaryKey($fieldName, $this);
			
		// General casting information for items in $db or $casting
		} else if($helper = $this->castingHelper($fieldName)) {
			$obj = Object::create_from_string($helper, $fieldName);
			$obj->setValue($this->$fieldName, $this->record, false);
			return $obj;
			
		// Special case for has_one relationships
		} else if(preg_match('/ID$/', $fieldName) && $this->has_one(substr($fieldName,0,-2))) {
			$val = (isset($this->record[$fieldName])) ? $this->record[$fieldName] : null;
			return DBField::create('ForeignKey', $val, $fieldName, $this);
			
		// Special case for ClassName
		} else if($fieldName == 'ClassName') {
			$val = get_class($this);
			return DBField::create('Varchar', $val, $fieldName, $this);
		}
	}

	/**
	 * Traverses to a DBField referenced by relationships between data objects.
	 * The path to the related field is specified with dot separated syntax (eg: Parent.Child.Child.FieldName)
	 *
	 * @param $fieldPath string
	 * @return DBField
	 */
	public function relObject($fieldPath) {
		$parts = explode('.', $fieldPath);
		$fieldName = array_pop($parts);
		$component = $this;
		foreach($parts as $relation) {
			if ($rel = $component->has_one($relation)) {
				$component = singleton($rel);
			} elseif ($rel = $component->has_many($relation)) {
				$component = singleton($rel);
			} elseif ($rel = $component->many_many($relation)) {
				$component = singleton($rel[1]);
			} elseif($className = $this->castingClass($relation)) {
				$component = $className;
			}
		}

		$object = $component->dbObject($fieldName);

		if (!($object instanceof DBField) && !($object instanceof DataList)) {
			// Todo: come up with a broader range of exception objects to describe differnet kinds of errors programatically
			throw new Exception("Unable to traverse to related object field [$fieldPath] on [$this->class]");
		}
		return $object;
	}

	/**
	 * Temporary hack to return an association name, based on class, to get around the mangle
	 * of having to deal with reverse lookup of relationships to determine autogenerated foreign keys.
	 * 
	 * @return String
	 */
	public function getReverseAssociation($className) {
		if (is_array($this->many_many())) {
			$many_many = array_flip($this->many_many());
			if (array_key_exists($className, $many_many)) return $many_many[$className];
		}
		if (is_array($this->has_many())) {
			$has_many = array_flip($this->has_many());
			if (array_key_exists($className, $has_many)) return $has_many[$className];
		}
		if (is_array($this->has_one())) {
			$has_one = array_flip($this->has_one());
			if (array_key_exists($className, $has_one)) return $has_one[$className];
		}
		
		return false;
	}

	/**
	 * @deprecated 3.0 Use DataObject::get and DataList to do your querying
	 */
	public function buildSQL($filter = "", $sort = "", $limit = "", $join = "", $restrictClasses = true, $having = "") {
		Deprecation::notice('3.0', 'Use DataObject::get and DataList to do your querying instead.');
		return $this->extendedSQL($filter, $sort, $limit, $join, $having);

	}
	
	/**
	 * Cache for the hairy bit of buildSQL
	 */
	private static $cache_buildSQL_query;

	/**
	 * @deprecated 3.0 Use DataObject::get and DataList to do your querying
	 */
	public function extendedSQL($filter = "", $sort = "", $limit = "", $join = ""){
		Deprecation::notice('3.0', 'Use DataObject::get and DataList to do your querying instead.');
		$dataList = DataObject::get($this->class, $filter, $sort, $join, $limit);
		return $dataList->dataQuery()->query();
	}

	/**
	 * Return all objects matching the filter
	 * sub-classes are automatically selected and included
	 *
	 * @param string $callerClass The class of objects to be returned
	 * @param string $filter A filter to be inserted into the WHERE clause.
	 * @param string|array $sort A sort expression to be inserted into the ORDER BY clause.  If omitted, self::$default_sort will be used.
	 * @param string $join A single join clause.  This can be used for filtering, only 1 instance of each DataObject will be returned.
	 * @param string|array $limit A limit expression to be inserted into the LIMIT clause.
	 * @param string $containerClass The container class to return the results in.
	 *
	 * @return mixed The objects matching the filter, in the class specified by $containerClass
	 */
	public static function get($callerClass, $filter = "", $sort = "", $join = "", $limit = null, $containerClass = "DataList") {
		// Todo: Determine if we can deprecate for 3.0.0 and use DI or something instead
		// Todo: Make the $containerClass method redundant
		if($containerClass != "DataList") user_error("The DataObject::get() \$containerClass argument has been deprecated", E_USER_NOTICE);
		$result = DataList::create($callerClass)->where($filter)->sort($sort);
		if($limit && strpos($limit, ',') !== false) {
			$limitArguments = explode(',', $limit);
			$result->limit($limitArguments[1],$limitArguments[0]);
		} elseif($limit) {
			$result->limit($limit);
		}
		if($join) $result = $result->join($join);
		$result->setModel(DataModel::inst());
		return $result;
	}
	
	/**
	 * @deprecated 3.0 Use DataObject::get and DataList to do your querying
	 */
	public function Aggregate($class = null) {
		Deprecation::notice('3.0', 'Use DataObject::get and DataList to do your querying instead.');

	    if($class) {
			$list = new DataList($class);
			$list->setModel(DataModel::inst());
		} else if(isset($this)) {
			$list = new DataList(get_class($this));
			$list->setModel($this->model);
		}
	    else throw new InvalidArgumentException("DataObject::aggregate() must be called as an instance method or passed a classname");
		return $list;
	}

	/**
	 * @deprecated 3.0 Use DataObject::get and DataList to do your querying
	 */
	public function RelationshipAggregate($relationship) {
		Deprecation::notice('3.0', 'Use DataObject::get and DataList to do your querying instead.');

	    return $this->$relationship();
	}

	/**
	 * The internal function that actually performs the querying for get().
	 * DataObject::get("Table","filter") is the same as singleton("Table")->instance_get("filter")
	 *
	 * @deprecated 3.0 Use DataObject::get and DataList to do your querying
	 *
	 * @param string $filter A filter to be inserted into the WHERE clause.
	 * @param string $sort A sort expression to be inserted into the ORDER BY clause.  If omitted, self::$default_sort will be used.
	 * @param string $join A single join clause.  This can be used for filtering, only 1 instance of each DataObject will be returned.
	 * @param string $limit A limit expression to be inserted into the LIMIT clause.
	 * @param string $containerClass The container class to return the results in.
	 *
	 * @return mixed The objects matching the filter, in the class specified by $containerClass
	 */
	public function instance_get($filter = "", $sort = "", $join = "", $limit="", $containerClass = "DataObjectSet") {
		Deprecation::notice('3.0', 'Use DataObject::get and DataList to do your querying instead.');
		return self::get($this->class, $filter, $sort, $join, $limit, $containerClass);
	}

	/**
	 * Take a database {@link SS_Query} and instanciate an object for each record.
	 * 
	 * @deprecated 3.0 Replaced by DataList
	 *
	 * @param SS_Query|array $records The database records, a {@link SS_Query} object or an array of maps.
	 * @param string $containerClass The class to place all of the objects into.
	 *
	 * @return mixed The new objects in an object of type $containerClass
	 */
	function buildDataObjectSet($records, $containerClass = "DataObjectSet", $query = null, $baseClass = null) {
		Deprecation::notice('3.0', 'Use DataList instead.');

		foreach($records as $record) {
			if(empty($record['RecordClassName'])) {
				$record['RecordClassName'] = $record['ClassName'];
			}
			if(class_exists($record['RecordClassName'])) {
				$results[] = new $record['RecordClassName']($record);
			} else {
				if(!$baseClass) {
					user_error("Bad RecordClassName '{$record['RecordClassName']}' and "
						. "\$baseClass not set", E_USER_ERROR);
				} else if(!is_string($baseClass) || !class_exists($baseClass)) {
					user_error("Bad RecordClassName '{$record['RecordClassName']}' and bad "
						. "\$baseClass '$baseClass not set", E_USER_ERROR);
				}
				$results[] = new $baseClass($record);
			}
		}

		if(isset($results)) {
			return new $containerClass($results);
		}
	}

	/**
	 * A cache used by get_one.
	 * @var array
	 */
	protected static $cache_get_one;

	/**
	 * Return the first item matching the given query.
	 * All calls to get_one() are cached.
	 *
	 * @param string $callerClass The class of objects to be returned
	 * @param string $filter A filter to be inserted into the WHERE clause
	 * @param boolean $cache Use caching
	 * @param string $orderby A sort expression to be inserted into the ORDER BY clause.
	 *
	 * @return DataObject The first item matching the query
	 */
	public static function get_one($callerClass, $filter = "", $cache = true, $orderby = "") {
		$SNG = singleton($callerClass);

		$cacheKey = "{$filter}-{$orderby}";
		if($extra = $SNG->extend('cacheKeyComponent')) {
			$cacheKey .= '-' . implode("-", $extra);
		}
		$cacheKey = md5($cacheKey);
		
		// Flush destroyed items out of the cache
		if($cache && isset(DataObject::$cache_get_one[$callerClass][$cacheKey]) && DataObject::$cache_get_one[$callerClass][$cacheKey] instanceof DataObject && DataObject::$cache_get_one[$callerClass][$cacheKey]->destroyed) {
			DataObject::$cache_get_one[$callerClass][$cacheKey
			] = false;
		}
		if(!$cache || !isset(DataObject::$cache_get_one[$callerClass][$cacheKey])) {
			$dl = DataList::create($callerClass)->where($filter)->sort($orderby);
			$dl->setModel(DataModel::inst());
			$item = $dl->First();

			if($cache) {
				DataObject::$cache_get_one[$callerClass][$cacheKey] = $item;
				if(!DataObject::$cache_get_one[$callerClass][$cacheKey]) {
					DataObject::$cache_get_one[$callerClass][$cacheKey] = false;
				}
			}
		}
		return $cache ? DataObject::$cache_get_one[$callerClass][$cacheKey] : $item;
	}

	/**
	 * Flush the cached results for all relations (has_one, has_many, many_many)
	 * Also clears any cached aggregate data
	 * 
	 * @param boolean $persistant When true will also clear persistant data stored in the Cache system.
	 *                            When false will just clear session-local cached data 
	 * 
	 */
	public function flushCache($persistant=true) {
		if($persistant) Aggregate::flushCache($this->class);
		
		if($this->class == 'DataObject') {
			DataObject::$cache_get_one = array();
			return;
		}

		$classes = ClassInfo::ancestry($this->class);
		foreach($classes as $class) {
			if(isset(self::$cache_get_one[$class])) unset(self::$cache_get_one[$class]);
		}
		
		$this->extend('flushCache');
		
		$this->componentCache = array();
	}

	static function flush_and_destroy_cache() {
		if(self::$cache_get_one) foreach(self::$cache_get_one as $class => $items) {
			if(is_array($items)) foreach($items as $item) {
				if($item) $item->destroy();
			}
		}
		self::$cache_get_one = array();
	}
	
	/**
	 * Reset internal caches, for example after test runs
	 */
	static function reset() {
		self::$cache_get_one = array();
		self::$cache_buildSQL_query = array();
	}

	/**
	 * Does the hard work for get_one()
	 *
	 * @deprecated 3.0 Use DataObject::get_one() instead
	 * 
	 * @uses DataExtension->augmentSQL()
	 *
	 * @param string $filter A filter to be inserted into the WHERE clause
	 * @param string $orderby A sort expression to be inserted into the ORDER BY clause.
	 * @return DataObject The first item matching the query
	 */
	public function instance_get_one($filter, $orderby = null) {
		Deprecation::notice('3.0', 'Use DataObject::get_one() instead.');
		return DataObject::get_one($this->class, $filter, true, $orderby);
	}

	/**
	 * Return the given element, searching by ID
	 *
	 * @param string $callerClass The class of the object to be returned
	 * @param int $id The id of the element
	 * @param boolean $cache See {@link get_one()}
	 *
	 * @return DataObject The element
	 */
	public static function get_by_id($callerClass, $id, $cache = true) {
		if(is_numeric($id)) {
			if(is_subclass_of($callerClass, 'DataObject')) {
				$baseClass = ClassInfo::baseDataClass($callerClass);
				return DataObject::get_one($callerClass,"\"$baseClass\".\"ID\" = $id", $cache);

				// This simpler code will be used by non-DataObject classes that implement DataObjectInterface
			} else {
				return DataObject::get_one($callerClass,"\"ID\" = $id", $cache);
			}
		} else {
			user_error("DataObject::get_by_id passed a non-numeric ID #$id", E_USER_WARNING);
		}
	}

	/**
	 * Get the name of the base table for this object
	 */
	public function baseTable() {
		$tableClasses = ClassInfo::dataClassesFor($this->class);
		return array_shift($tableClasses);
	}

	//-------------------------------------------------------------------------------------------//

	/**
	 * Return the database indexes on this table.
	 * This array is indexed by the name of the field with the index, and
	 * the value is the type of index.
	 */
	public function databaseIndexes() {
		$has_one = $this->uninherited('has_one',true);
		$classIndexes = $this->uninherited('indexes',true);
		//$fileIndexes = $this->uninherited('fileIndexes', true);

		$indexes = array();

		if($has_one) {
			foreach($has_one as $relationshipName => $fieldType) {
				$indexes[$relationshipName . 'ID'] = true;
			}
		}

		if($classIndexes) {
			foreach($classIndexes as $indexName => $indexType) {
				$indexes[$indexName] = $indexType;
			}
		}

		if(get_parent_class($this) == "DataObject") {
			$indexes['ClassName'] = true;
		}

		return $indexes;
	}

	/**
	 * Check the database schema and update it as necessary.
	 * 
	 * @uses DataExtension->augmentDatabase()
	 */
	public function requireTable() {
		// Only build the table if we've actually got fields
		$fields = self::database_fields($this->class);
		$extensions = self::database_extensions($this->class);
		
		$indexes = $this->databaseIndexes();

		if($fields) {
			$hasAutoIncPK = ($this->class == ClassInfo::baseDataClass($this->class));
			DB::requireTable($this->class, $fields, $indexes, $hasAutoIncPK, $this->stat('create_table_options'), $extensions);
		} else {
			DB::dontRequireTable($this->class);
		}

		// Build any child tables for many_many items
		if($manyMany = $this->uninherited('many_many', true)) {
			$extras = $this->uninherited('many_many_extraFields', true);
			foreach($manyMany as $relationship => $childClass) {
				// Build field list
				$manymanyFields = array(
					"{$this->class}ID" => "Int",
				(($this->class == $childClass) ? "ChildID" : "{$childClass}ID") => "Int",
				);
				if(isset($extras[$relationship])) {
					$manymanyFields = array_merge($manymanyFields, $extras[$relationship]);
				}

				// Build index list
				$manymanyIndexes = array(
					"{$this->class}ID" => true,
				(($this->class == $childClass) ? "ChildID" : "{$childClass}ID") => true,
				);
				
				DB::requireTable("{$this->class}_$relationship", $manymanyFields, $manymanyIndexes, true, null, $extensions);
			}
		}

		// Let any extentions make their own database fields
		$this->extend('augmentDatabase', $dummy);
	}

	/**
	 * Add default records to database. This function is called whenever the
	 * database is built, after the database tables have all been created. Overload
	 * this to add default records when the database is built, but make sure you
	 * call parent::requireDefaultRecords().
	 * 
	 * @uses DataExtension->requireDefaultRecords()
	 */
	public function requireDefaultRecords() {
		$defaultRecords = $this->stat('default_records');

		if(!empty($defaultRecords)) {
			$hasData = DataObject::get_one($this->class);
			if(!$hasData) {
				$className = $this->class;
				foreach($defaultRecords as $record) {
					$obj = $this->model->$className->newObject($record);
					$obj->write();
				}
				DB::alteration_message("Added default records to $className table","created");
			}
		}
		
		// Let any extentions make their own database default data
		$this->extend('requireDefaultRecords', $dummy);
	}
	
	/**
	 * @deprecated 3.0 Use DataObject::database_fields() instead
	 * @see DataObject::database_fields()
	 */
	public function databaseFields() {
		Deprecation::notice('3.0', 'Use DataObject::database_fields() instead.');
		return self::database_fields($this->class);
	}
	
	/**
	 * @deprecated 3.0 Use DataObject::custom_database_fields() instead
	 * @see DataObject::custom_database_fields()
	 */
	public function customDatabaseFields() {
		Deprecation::notice('3.0', 'Use DataObject::custom_database_fields() instead.');
		return self::custom_database_fields($this->class);
	}
	
	/**
	 * Returns fields bu traversing the class heirachy in a bottom-up direction.
	 *
	 * Needed to avoid getCMSFields being empty when customDatabaseFields overlooks
	 * the inheritance chain of the $db array, where a child data object has no $db array,
	 * but still needs to know the properties of its parent. This should be merged into databaseFields or
	 * customDatabaseFields.
	 *
	 * @todo review whether this is still needed after recent API changes
	 */
	public function inheritedDatabaseFields() {
		$fields     = array();
		$currentObj = $this->class;
		
		while($currentObj != 'DataObject') {
			$fields     = array_merge($fields, self::custom_database_fields($currentObj));
			$currentObj = get_parent_class($currentObj);
		}
		
		return (array) $fields;
	}

	/**
	 * Get the default searchable fields for this object,
	 * as defined in the $searchable_fields list. If searchable
	 * fields are not defined on the data object, uses a default
	 * selection of summary fields.
	 *
	 * @return array
	 */
	public function searchableFields() {
		// can have mixed format, need to make consistent in most verbose form
		$fields = $this->stat('searchable_fields');
		
		$labels = $this->fieldLabels();
		
		// fallback to summary fields
		if(!$fields) $fields = array_keys($this->summaryFields());
		
		// we need to make sure the format is unified before
		// augmenting fields, so extensions can apply consistent checks
		// but also after augmenting fields, because the extension
		// might use the shorthand notation as well

		// rewrite array, if it is using shorthand syntax
		$rewrite = array();
		foreach($fields as $name => $specOrName) {
			$identifer = (is_int($name)) ? $specOrName : $name;

			if(is_int($name)) {
				// Format: array('MyFieldName')
				$rewrite[$identifer] = array();
			} elseif(is_array($specOrName)) {
				// Format: array('MyFieldName' => array(
				//   'filter => 'ExactMatchFilter',
				//   'field' => 'NumericField', // optional
				//   'title' => 'My Title', // optiona.
				// ))
				$rewrite[$identifer] = array_merge(
					array('filter' => $this->relObject($identifer)->stat('default_search_filter_class')),
					(array)$specOrName
				);
			} else {
				// Format: array('MyFieldName' => 'ExactMatchFilter')
				$rewrite[$identifer] = array(
					'filter' => $specOrName,
				);
			}
			if(!isset($rewrite[$identifer]['title'])) {
				$rewrite[$identifer]['title'] = (isset($labels[$identifer])) ? $labels[$identifer] : FormField::name_to_label($identifer);
			}
			if(!isset($rewrite[$identifer]['filter'])) {
				$rewrite[$identifer]['filter'] = 'PartialMatchFilter';
			}
		}

		$fields = $rewrite;
		
		// apply DataExtensions if present
		$this->extend('updateSearchableFields', $fields);

		return $fields;
	}
	
	/**
	 * Get any user defined searchable fields labels that
	 * exist. Allows overriding of default field names in the form
	 * interface actually presented to the user.
	 *
	 * The reason for keeping this separate from searchable_fields,
	 * which would be a logical place for this functionality, is to
	 * avoid bloating and complicating the configuration array. Currently
	 * much of this system is based on sensible defaults, and this property
	 * would generally only be set in the case of more complex relationships
	 * between data object being required in the search interface.
	 *
	 * Generates labels based on name of the field itself, if no static property 
	 * {@link self::field_labels} exists.
	 *
	 * @uses $field_labels
	 * @uses FormField::name_to_label()
	 *
	 * @param boolean $includerelations a boolean value to indicate if the labels returned include relation fields
	 * 
	 * @return array|string Array of all element labels if no argument given, otherwise the label of the field
	 */
	public function fieldLabels($includerelations = true) {
		$customLabels = $this->stat('field_labels');
		$autoLabels = array();
		
		// get all translated static properties as defined in i18nCollectStatics()
		$ancestry = ClassInfo::ancestry($this->class);
		$ancestry = array_reverse($ancestry);
		if($ancestry) foreach($ancestry as $ancestorClass) {
			if($ancestorClass == 'ViewableData') break;
			$types = array(
				'db'        => (array) Object::uninherited_static($ancestorClass, 'db'),
			);
			if($includerelations){
				$types['has_one'] = (array)singleton($ancestorClass)->uninherited('has_one', true);
				$types['has_many'] = (array)singleton($ancestorClass)->uninherited('has_many', true);
				$types['many_many'] = (array)singleton($ancestorClass)->uninherited('many_many', true);
			}
			foreach($types as $type => $attrs) {
				foreach($attrs as $name => $spec)
				$autoLabels[$name] = _t("{$ancestorClass}.{$type}_{$name}",FormField::name_to_label($name));
 			}
 		}

		$labels = array_merge((array)$autoLabels, (array)$customLabels);
		
		$this->extend('updateFieldLabels', $labels);

		return $labels;
	}
	
	/**
	 * Get a human-readable label for a single field,
	 * see {@link fieldLabels()} for more details.
	 * 
	 * @uses fieldLabels()
	 * @uses FormField::name_to_label()
	 * 
	 * @param string $name Name of the field
	 * @return string Label of the field
	 */
	public function fieldLabel($name) {
		$labels = $this->fieldLabels();
		return (isset($labels[$name])) ? $labels[$name] : FormField::name_to_label($name);
	}

	/**
	 * Get the default summary fields for this object.
	 *
	 * @todo use the translation apparatus to return a default field selection for the language
	 *
	 * @return array
	 */
	public function summaryFields(){

		$fields = $this->stat('summary_fields');

		// if fields were passed in numeric array,
		// convert to an associative array
		if($fields && array_key_exists(0, $fields)) {
			$fields = array_combine(array_values($fields), array_values($fields));
		}

		if (!$fields) {
			$fields = array();
			// try to scaffold a couple of usual suspects
			if ($this->hasField('Name')) $fields['Name'] = 'Name';
			if ($this->hasDataBaseField('Title')) $fields['Title'] = 'Title';
			if ($this->hasField('Description')) $fields['Description'] = 'Description';
			if ($this->hasField('FirstName')) $fields['FirstName'] = 'First Name';
		}
		$this->extend("updateSummaryFields", $fields);
		
		// Final fail-over, just list ID field
		if(!$fields) $fields['ID'] = 'ID';
		
		return $fields;
	}

	/**
	 * Defines a default list of filters for the search context.
	 *
	 * If a filter class mapping is defined on the data object,
	 * it is constructed here. Otherwise, the default filter specified in
	 * {@link DBField} is used.
	 *
	 * @todo error handling/type checking for valid FormField and SearchFilter subclasses?
	 *
	 * @return array
	 */
	public function defaultSearchFilters() {
		$filters = array();
		foreach($this->searchableFields() as $name => $spec) {
			$filterClass = $spec['filter'];
			// if $filterClass is not set a name of any subclass of SearchFilter than assing 'PartiailMatchFilter' to it
			if (!is_subclass_of($filterClass, 'SearchFilter')) {
				$filterClass = 'PartialMatchFilter';
			}
			$filters[$name] = new $filterClass($name);
		}
		return $filters;
	}

	/**
	 * @return boolean True if the object is in the database
	 */
	public function isInDB() {
		return is_numeric( $this->ID ) && $this->ID > 0;
	}

	/*
	 * @ignore
	 */
	private static $subclass_access = true; 
	
	/**
	 * Temporarily disable subclass access in data object qeur
	 */
	static function disable_subclass_access() {
		self::$subclass_access = false;
	}
	static function enable_subclass_access() {
		self::$subclass_access = true;
	}
	
	//-------------------------------------------------------------------------------------------//

	/**
	 * Database field definitions.
	 * This is a map from field names to field type. The field
	 * type should be a class that extends .
	 * @var array
	 */
	public static $db = null;

	/**
	 * Use a casting object for a field. This is a map from
	 * field name to class name of the casting object.
	 * @var array
	 */
	public static $casting = array(
		"LastEdited" => "SS_Datetime",
		"Created" => "SS_Datetime",
		"Title" => 'Text',
	);
	
	/**
	 * Specify custom options for a CREATE TABLE call.
	 * Can be used to specify a custom storage engine for specific database table.
	 * All options have to be keyed for a specific database implementation,
	 * identified by their class name (extending from {@link SS_Database}).
	 * 
	 * <code>
	 * array(
	 * 	'MySQLDatabase' => 'ENGINE=MyISAM'
	 * )
	 * </code>
	 *
	 * Caution: This API is experimental, and might not be
	 * included in the next major release. Please use with care.
	 * 
	 * @var array
	 */
	static $create_table_options = array(
		'MySQLDatabase' => 'ENGINE=InnoDB'
	);

	/**
	 * If a field is in this array, then create a database index
	 * on that field. This is a map from fieldname to index type.
	 * See {@link SS_Database->requireIndex()} and custom subclasses for details on the array notation.
	 * 
	 * @var array
	 */
	public static $indexes = null;

	/**
	 * Inserts standard column-values when a DataObject
	 * is instanciated. Does not insert default records {@see $default_records}.
	 * This is a map from fieldname to default value.
	 * 
	 *  - If you would like to change a default value in a sub-class, just specify it.
	 *  - If you would like to disable the default value given by a parent class, set the default value to 0,'',or false in your
	 *    subclass.  Setting it to null won't work.
	 * 
	 * @var array
	 */
	public static $defaults = null;

	/**
	 * Multidimensional array which inserts default data into the database
	 * on a db/build-call as long as the database-table is empty. Please use this only
	 * for simple constructs, not for SiteTree-Objects etc. which need special
	 * behaviour such as publishing and ParentNodes.
	 *
	 * Example:
	 * array(
	 * 	array('Title' => "DefaultPage1", 'PageTitle' => 'page1'),
	 * 	array('Title' => "DefaultPage2")
	 * ).
	 *
	 * @var array
	 */
	public static $default_records = null;

	/**
	 * One-to-zero relationship defintion. This is a map of component name to data type. In order to turn this into a
	 * true one-to-one relationship you can add a {@link DataObject::$belongs_to} relationship on the child class.
	 *
	 * Note that you cannot have a has_one and belongs_to relationship with the same name.
	 *
	 *	@var array
	 */
	public static $has_one = null;
	
	/**
	 * A meta-relationship that allows you to define the reverse side of a {@link DataObject::$has_one}.
	 *
	 * This does not actually create any data structures, but allows you to query the other object in a one-to-one
	 * relationship from the child object. If you have multiple belongs_to links to another object you can use the
	 * syntax "ClassName.HasOneName" to specify which foreign has_one key on the other object to use.
	 *
	 * Note that you cannot have a has_one and belongs_to relationship with the same name.
	 *
	 * @var array
	 */
	public static $belongs_to;
	
	/**
	 * This defines a one-to-many relationship. It is a map of component name to the remote data class.
	 *
	 * This relationship type does not actually create a data structure itself - you need to define a matching $has_one
	 * relationship on the child class. Also, if the $has_one relationship on the child class has multiple links to this
	 * class you can use the syntax "ClassName.HasOneRelationshipName" in the remote data class definition to show
	 * which foreign key to use.
	 *
	 * @var array
	 */
	public static $has_many = null;

	/**
	 * many-many relationship definitions.
	 * This is a map from component name to data type.
	 * @var array
	 */
	public static $many_many = null;

	/**
	 * Extra fields to include on the connecting many-many table.
	 * This is a map from field name to field type.
	 * 
	 * Example code:
	 * <code>
	 * public static $many_many_extraFields = array(
	 * 	'Members' => array(
	 *			'Role' => 'Varchar(100)'
	 *		)
	 * );
	 * </code>
	 * 
	 * @var array
	 */
	public static $many_many_extraFields = null;

	/**
	 * The inverse side of a many-many relationship.
	 * This is a map from component name to data type.
	 * @var array
	 */
	public static $belongs_many_many = null;

	/**
	 * The default sort expression. This will be inserted in the ORDER BY
	 * clause of a SQL query if no other sort expression is provided.
	 * @var string
	 */
	public static $default_sort = null;

	/**
	 * Default list of fields that can be scaffolded by the ModelAdmin
	 * search interface.
	 *
	 * Overriding the default filter, with a custom defined filter:
	 * <code>
	 * 	static $searchable_fields = array(
	 * 	   "Name" => "PartialMatchFilter"
	 *  );
	 * </code>
	 * 
	 * Overriding the default form fields, with a custom defined field.
	 * The 'filter' parameter will be generated from {@link DBField::$default_search_filter_class}.
	 * The 'title' parameter will be generated from {@link DataObject->fieldLabels()}.
	 * <code>
	 * 	static $searchable_fields = array(
	 * 	   "Name" => array(
	 * 			"field" => "TextField"
	 * 		)
	 *  );
	 * </code>
	 *
	 * Overriding the default form field, filter and title:
	 * <code>
	 * 	static $searchable_fields = array(
	 * 	   "Organisation.ZipCode" => array(
	 * 			"field" => "TextField", 
	 * 			"filter" => "PartialMatchFilter",
	 * 			"title" => 'Organisation ZIP'
	 * 		)
	 *  );
	 * </code>
	 */
	public static $searchable_fields = null;

	/**
	 * User defined labels for searchable_fields, used to override
	 * default display in the search form.
	 */
	public static $field_labels = null;

	/**
	 * Provides a default list of fields to be used by a 'summary'
	 * view of this object.
	 */
	public static $summary_fields = null;
	
	/**
	 * Provides a list of allowed methods that can be called via RESTful api.
	 */
	public static $allowed_actions = null;
	
	/**
	 * Collect all static properties on the object
	 * which contain natural language, and need to be translated.
	 * The full entity name is composed from the class name and a custom identifier.
	 * 
	 * @return array A numerical array which contains one or more entities in array-form.
	 * Each numeric entity array contains the "arguments" for a _t() call as array values:
	 * $entity, $string, $priority, $context.
	 */
	public function provideI18nEntities() {
		$entities = array();
		
		$entities["{$this->class}.SINGULARNAME"] = array(
			$this->singular_name(),
			PR_MEDIUM,
			'Singular name of the object, used in dropdowns and to generally identify a single object in the interface'
		);

		$entities["{$this->class}.PLURALNAME"] = array(
			$this->plural_name(),
			PR_MEDIUM,
			'Pural name of the object, used in dropdowns and to generally identify a collection of this object in the interface'
		);
		
		return $entities;
	}
	
	/**
 	 * Returns true if the given method/parameter has a value
 	 * (Uses the DBField::hasValue if the parameter is a database field)
 	 * 
	 * @param string $field The field name
	 * @param array $arguments
	 * @param bool $cache
 	 * @return boolean
 	 */
 	function hasValue($field, $arguments = null, $cache = true) {
 		$obj = $this->dbObject($field);
 		if($obj) {
 			return $obj->hasValue();
 		} else {
 			return parent::hasValue($field, $arguments, $cache);
 		}
 	}

}