API CHANGE: add a remote relation class getter to DataObject

model/DataObject.php

@@ -1342,7 +1342,38 @@ public function getComponentsQuery($componentName, $filter = "", $sort = "", $jo
 
 		return singleton($componentClass)->extendedSQL($combinedFilter, $sort, $limit, $join);
 	}
-
+
+	/**
+	 * Find the foreign class of a relation on this DataObject, regardless of the relation type.
+	 *
+	 * @param $relationName Relation name.
+	 * @return string Class name, or null if not found.
+	 */
+	public function getRelationClass($relationName) {
+		// Go through all relationship configuration fields.
+		$candidates = array_merge(
+			($relations = Config::inst()->get($this->class, 'has_one')) ? $relations : array(),
+			($relations = Config::inst()->get($this->class, 'has_many')) ? $relations : array(),
+			($relations = Config::inst()->get($this->class, 'many_many')) ? $relations : array(),
+			($relations = Config::inst()->get($this->class, 'belongs_many_many')) ? $relations : array(),
+			($relations = Config::inst()->get($this->class, 'belongs_to')) ? $relations : array()
+		);
+
+		if (isset($candidates[$relationName])) {
+			$remoteClass = $candidates[$relationName];
+
+			// If dot notation is present, extract just the first part that contains the class.
+			if(($fieldPos = strpos($remoteClass, '.'))!==false) {
+				return substr($remoteClass, 0, $fieldPos);
+			}
+
+			// Otherwise just return the class
+			return $remoteClass;
+		}
+
+		return null;
+	}
+
 	/**
 	 * 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'.

tests/model/DataObjectTest.php

@@ -183,6 +183,15 @@ function testGetSubclassFields() {
 		$this->assertEquals($this->idFromFixture('DataObjectTest_Team', 'team1'), $captain1->FavouriteTeamID);
 	}
 
+	function testGetRelationClass() {
+		$obj = new DataObjectTest_Player();
+		$this->assertEquals(singleton('DataObjectTest_Player')->getRelationClass('FavouriteTeam'), 'DataObjectTest_Team', 'has_one is properly inspected');
+		$this->assertEquals(singleton('DataObjectTest_Company')->getRelationClass('CurrentStaff'), 'DataObjectTest_Staff', 'has_many is properly inspected');
+		$this->assertEquals(singleton('DataObjectTest_Team')->getRelationClass('Players'), 'DataObjectTest_Player', 'many_many is properly inspected');
+		$this->assertEquals(singleton('DataObjectTest_Player')->getRelationClass('Teams'), 'DataObjectTest_Team', 'belongs_many_many is properly inspected');
+		$this->assertEquals(singleton('DataObjectTest_CEO')->getRelationClass('Company'), 'DataObjectTest_Company', 'belongs_to is properly inspected');
+	}
+
 	function testGetHasOneRelations() {
 		$captain1 = $this->objFromFixture("DataObjectTest_Player", "captain1");
 		/* There will be a field called (relname)ID that contains the ID of the object linked to via the has_one relation */