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DataExtension

Introduction

Extensions allow for adding additional functionality to a [api:DataObject] or modifying existing functionality without the hassle of creating a subclass.

Usage

Extensions are defined as subclasses of either [api:DataExtension] for extending a [api:DataObject] subclass or the [api:Extension] class for non DataObject subclasses (such as Controllers)

:::php
<?php
// mysite/code/MyMemberExtension.php

class MyMemberExtension extends DataExtension {

}

This defines your own extension where we can add our own functions, database fields or other properties. After this class has been created, it does not yet apply it to your object. Next you need to tell SilverStripe what class you want to extend.

Adding a extension to a built-in class

For example, you may might want to add a MyMemberExtension class to the [api:Member] object to provide a custom method.

In order to active this extension, you need to add the following to your config.yml.

:::yml
Member:
  extensions:
    - MyMemberExtension

Alternatively, you can add extensions through PHP code (in your _config.php file).

:::php
Member::add_extension('MyMemberExtension');

Extending code to allow for extensions

If you're providing a module or working on code that may need to be extended by other code, it can provide a hook which allows an Extension to modify the results. This is done through the [api:Object->extend()] method.

:::php
public function myFunc() {
	$foo = // ..

	$this->extend('alterFoo', $foo);

	return $foo;
}

In this example, the myFunc() method adds a hook to allow DataExtension subclasses added to the instance to define an alterFoo($foo) method to modify the result of the method.

The $foo parameter is passed by reference, as it is an object.

Accessing the original Object from an Extension

In your extension class you can refer to the source object through the owner property on the class.

:::php
<?php

class MyMemberExtension extends DataExtension {

	public function alterFoo($foo) {
		// outputs the original class
		var_dump($this->owner);
	}
}

Checking to see if an Object has an Extension

To see what extensions are currently enabled on an object, you can use [api:Object->getExtensionInstances()] and [api:Object->hasExtension($extension)].

Implementation

Adding extra database fields

Extra database fields can be added with a extension in the same manner as if they were placed on the DataObject class they're applied to. These will be added to the table of the base object - the extension will actually edit the $db, $has_one, etc static variables on load.

The function should return a map where the keys are the names of the static variables to update:

:::php
<?php

class MyMemberExtension extends DataExtension {

	private static $db = array(
		'Position' => 'Varchar',
	);

	private static $has_one = array(
		'Image' => 'Image',
	);
}

Modifying CMS Fields

The member class demonstrates an extension that allows you to update the default CMS fields for an object in an extension:

:::php
<?php

class MyMemberExtension extends DataExtension {

	private static $db = array(
		'Position' => 'Varchar',
	);

	private static $has_one = array(
		'Image' => 'Image',
	);

	public function updateCMSFields(FieldList $fields) {
  		$fields->push(new TextField('Position'));
  		$fields->push(new UploadField('Image', 'Profile Image'));
	}
}

Adding/modifying fields prior to extensions

User code can intervene in the process of extending cms fields by using beforeUpdateCMSFields in its implementation of getCMSFields. This can be useful in cases where user code will add fields to a dataobject that should be present in the $fields parameter when passed to updateCMSFields in extensions.

This method is preferred to disabling, enabling, and calling cms field extensions manually.

:::php
function getCMSFields() {
	$this->beforeUpdateCMSFields(function($fields) {
		// Include field which must be present when updateCMSFields is called on extensions
		$fields->addFieldToTab("Root.Main", new TextField('Detail', 'Details', null, 255));
	});

	$fields = parent::getCMSFields();
	// ... additional fields here
	return $fields;
}

Object extension injection points

Object now has two additional methods, beforeExtending and afterExtending, each of which takes a method name and a callback to be executed immediately before and after Object::extend() is called on extensions.

This is useful in many cases where working with modules such as Translatable which operate on DataObject fields that must exist in the FieldList at the time that $this->extend('UpdateCMSFields') is called.

Please note that each callback is only ever called once, and then cleared, so multiple extensions to the same function require that a callback is registered each time, if necessary.

Example: A class that wants to control default values during object initialization. The code needs to assign a value if not specified in self::$defaults, but before extensions have been called:

:::php
function __construct() {
	$self = $this;

	$this->beforeExtending('populateDefaults', function() uses ($self) {
		if(empty($self->MyField)) {
			$self->MyField = 'Value we want as a default if not specified in $defaults, but set before extensions';
		}
	});

	parent::__construct();
}

Custom database generation

Some extensions are designed to transparently add more sophisticated data-collection capabilities to your DataObject. For example, [api:Versioned] adds version tracking and staging to any DataObject that it is applied to.

To do this, define an augmentDatabase() method on your extension. This will be called when the database is rebuilt.

You can query $this->owner for information about the data object, such as the fields it has
You can use DB::requireTable($tableName, $fieldList, $indexList) to set up your new tables. This function takes care of creating, modifying, or leaving tables as required, based on your desired schema.

Custom write queries

If you have customised the generated database, then you probably want to change the way that writes happen. This isused by [api:Versioned] to get an entry written in ClassName_versions whenever an insert/update happens.

To do this, define the augmentWrite(&$manipulation) method. This method is passed a manipulation array representing the write about to happen, and is able to amend this as desired, since it is passed by reference.

Custom relation queries

The other queries that you will want to customise are the selection queries, called by get & get_one. For example, the Versioned object has code to redirect every request to ClassName_live, if you are browsing the live site.

To do this, define the augmentSQL(SQLSelect $query) method. Again, the $query object is passed by reference and can be modified as needed by your method. Instead of a manipulation array, we have a [api:SQLSelect] object.

Additional methods

The other thing you may want to do with a extension is provide a method that can be called on the [api:DataObject] that is being extended. For instance, you may add a publish() method to every [api:DataObject] that is extended with [api:Versioned].

This is as simple as defining a method called publish() on your extension. Bear in mind, however, that instead of $this, you should be referring to $this->owner.

$this = The [api:DataExtension] object.
$this->owner = The related [api:DataObject] object.

If you want to add your own internal properties, you can add this to the [api:DataExtension], and these will be referred to as $this->propertyName.
Every [api:DataObject] has an associated [api:DataExtension] instance for each class that it is extended by.

:::php
<?php

class Customer extends DataObject {

	private static $has_one = array(
		'Account' => 'Account'
	);

	private static $extensions = array(
		'CustomerWorkflow'
	);

}

class Account extends DataObject {

	private static $db = array(
		'IsMarkedForDeletion'=>'Boolean'
	);

	private static $has_many = array(
		'Customers' => 'Customer'
	);
}

class CustomerWorkflow extends DataExtension {

	public function IsMarkedForDeletion() {
		return (bool) $this->owner->Account()->IsMarkedForDeletion;
	}
}

API Documentation

[api:Extension]
[api:DataExtension]

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