API CHANGE: Added GridField::addDataFields() to allow the definition of custom callbacks to be used by all GridField components.

API CHANGE: Added GridField::getDataFieldValue() to encapsulate field lookup for all components.
API CHANGE: Allow 'callback' key to be specified in a GridFieldDataColumn column info.  In this case, title should be put as the 'title' key of a map rather than simply the column info.

forms/gridfield/GridField.php

@@ -57,6 +57,11 @@ class GridField extends FormField {
 	 */
 	protected $columnDispatch = null;
 	
+	/**
+	 * Map of callbacks for custom data fields
+	 */
+	protected $customDataFields = array();
+
 	protected $name = '';
 
 	/**
@@ -412,6 +417,30 @@ class GridField extends FormField {
 		}
 	}
 	
+	/**
+	 * Add additional calculated data fields to be used on this GridField
+	 * @param array $fields a map of fieldname to callback.  The callback will bed passed the record as an argument.
+	 */
+	public function addDataFields($fields) {
+		if($this->customDataFields) $this->customDataFields = array_merge($this->customDataFields, $fields);
+		else $this->customDataFields = $fields;		
+	}
+	
+	/**
+	 * Get the value of a named field  on the given record.
+	 * Use of this method ensures that any special rules around the data for this gridfield are followed.
+	 */
+	public function getDataFieldValue($record, $fieldName) {
+		// Custom callbacks
+		if(isset($this->customDataFields[$fieldName])) {
+			$callback = $this->customDataFields[$fieldName];
+			return $callback($record);
+		}
+		
+		// Default implementation
+		return $record->relField($fieldName);
+	}
+
 	/**
 	 * Get extra columns attributes used as HTML attributes
 	 *

forms/gridfield/GridFieldDataColumns.php

@@ -118,11 +118,18 @@ class GridFieldDataColumns implements GridField_ColumnProvider {
 	 * @return string HTML for the column. Return NULL to skip.
 	 */
 	public function getColumnContent($gridField, $record, $columnName) {
+		// Find the data column for the given named column
+		$columns = $this->getDisplayFields($gridField);
+		$columnInfo = $columns[$columnName];
+		
+		// Allow callbacks
+		if(is_array($columnInfo) && isset($columnInfo['callback'])) {
+			$method = $columnInfo['callback'];
+			$value = Convert::raw2xml($method($record));
+		
 		// This supports simple FieldName syntax
-		if(strpos($columnName, '.') === false) {
-			$value = $record->XML_val($columnName);
 		} else {
-			$value = $this->getValueFromRelation($record, $columnName);
+			$value = Convert::raw2xml($gridField->getDataFieldValue($record, $columnName));
 		}
 
 		$value = $this->castValue($gridField, $columnName, $value);
@@ -154,8 +161,16 @@ class GridFieldDataColumns implements GridField_ColumnProvider {
 	 */
 	public function getColumnMetadata($gridField, $column) {
 		$columns = $this->getDisplayFields($gridField);
+		
+		$title = null;
+		if(is_string($columns[$column])) {
+			$title = $columns[$column];
+		} else if(is_array($columns[$column]) && isset($columns[$column]['title'])) {
+			$title = $columns[$column]['title'];
+		}
+		
 		return array(
-			'title' => $columns[$column],
+			'title' => $title,
 		);
 	}
 	

forms/gridfield/GridFieldExportButton.php

@@ -138,7 +138,7 @@ class GridFieldExportButton implements GridField_HTMLProvider, GridField_ActionP
 
 					$value = $columnHeader($relObj);
 				} else {
-					$value = $item->relField($columnSource);
+					$value = $gridField->getDataFieldValue($item, $columnSource);
 				}
 
 				$value = str_replace(array("\r", "\n"), "\n", $value);

forms/gridfield/GridFieldPrintButton.php

@@ -115,7 +115,7 @@ class GridFieldPrintButton implements GridField_HTMLProvider, GridField_ActionPr
 		foreach($items as $item) {
 			$itemRow = new ArrayList();
 			foreach($printColumns as $field => $label) {
-				$value = $item->relField($field);
+				$value = $gridField->getDataFieldValue($item, $field);
 				$itemRow->push(
 					new ArrayData(array(
 						"CellString" => $value,