Index: Classes/Persistence/Backend.php
===================================================================
--- Classes/Persistence/Backend.php	(revision 3926)
+++ Classes/Persistence/Backend.php	(working copy)
@@ -704,13 +704,18 @@
 			$columnMap->getParentKeyFieldName() => (int)$parentObject->getUid(),
 			$columnMap->getChildKeyFieldName() => (int)$object->getUid(),
 			$columnMap->getChildSortByFieldName() => !is_null($sortingPosition) ? (int)$sortingPosition : 0
-			);
-		$relationTableName = $columnMap->getRelationTableName();
-		// FIXME Reenable support for tablenames
-		// $childTableName = $columnMap->getChildTableName();
-		// if (isset($childTableName)) {
-		// 	$row['tablenames'] = $childTableName;
-		// }
+		);
+
+			// support for "tablenames" column
+		if ($columnMap->getRelationTableRelatedTableColumnName() !== NULL) {
+			if ($columnMap->isMultiColumnRelation() === TRUE) {
+				$tableName = $this->dataMapper->getDataMap(get_class($object))->getTableName();
+			} else {
+				$tableName = $dataMap->getTableName();
+			}
+			$row[$columnMap->getRelationTableRelatedTableColumnName()] = $tableName;
+		}
+
 		if ($columnMap->getRelationTablePageIdColumnName() !== NULL) {
 			$row[$columnMap->getRelationTablePageIdColumnName()] = $this->determineStoragePageIdForNewRecord();
 		}
@@ -722,6 +727,7 @@
 			}
 		}
 
+		$relationTableName = $columnMap->getRelationTableName();
 		$res = $this->storageBackend->addRow(
 			$relationTableName,
 			$row,
@@ -745,10 +751,7 @@
 			$columnMap->getParentKeyFieldName() => (int)$parentObject->getUid()
 		);
 
-		$relationTableMatchFields = $columnMap->getRelationTableMatchFields();
-		if (is_array($relationTableMatchFields) && count($relationTableMatchFields) > 0) {
-			$relationMatchFields = array_merge($relationTableMatchFields,$relationMatchFields);
-		}
+		$this->addDefaultMatchFieldsToRelationMatchFields($columnMap, $relationMatchFields);
 
 		$res = $this->storageBackend->removeRow(
 			$relationTableName,
@@ -769,12 +772,17 @@
 		$dataMap = $this->dataMapper->getDataMap(get_class($parentObject));
 		$columnMap = $dataMap->getColumnMap($parentPropertyName);
 		$relationTableName = $columnMap->getRelationTableName();
+
+		$relationMatchFields = array(
+			$columnMap->getParentKeyFieldName() => (int)$parentObject->getUid(),
+			$columnMap->getChildKeyFieldName() => (int)$relatedObject->getUid(),
+		);
+
+		$this->addDefaultMatchFieldsToRelationMatchFields($columnMap, $relationMatchFields);
+
 		$res = $this->storageBackend->removeRow(
 			$relationTableName,
-			array(
-				$columnMap->getParentKeyFieldName() => (int)$parentObject->getUid(),
-				$columnMap->getChildKeyFieldName() => (int)$relatedObject->getUid(),
-				),
+			$relationMatchFields,
 			FALSE);
 		return $res;
 	}
@@ -809,11 +817,11 @@
 	}
 
 	/**
-	 * Returns a table row to be inserted or updated in the database
+	 * Adds common DB fields like creationDate, storagePids etc. to a database row
 	 *
-	 * @param Tx_Extbase_Persistence_Mapper_DataMap $dataMap The appropriate data map representing a database table
-	 * @param array $properties The properties of the object
-	 * @return array A single row to be inserted in the database
+	 * @param Tx_Extbase_DomainObject_DomainObjectInterface $object The related domain object the fields should be added for
+	 * @param array $row The database row the fields should get added to
+	 * @return void
 	 */
 	protected function addCommonFieldsToRow(Tx_Extbase_DomainObject_DomainObjectInterface $object, array &$row) {
 		$className = get_class($object);
@@ -833,6 +841,25 @@
 	}
 
 	/**
+	 * Adds default matchFields to the passed relationRow array which will be used in queries
+	 *
+	 * @param Tx_Extbase_Persistence_Mapper_ColumnMap $columnMap The column map representing the related database column
+	 * @param array $relationRow The relation row the fields should get added to
+	 * @return void
+	 */
+	protected function addDefaultMatchFieldsToRelationMatchFields(Tx_Extbase_Persistence_Mapper_ColumnMap $columnMap, array &$relationMatchFields) {
+		$relationTableMatchFields = $columnMap->getRelationTableMatchFields();
+		if (is_array($relationTableMatchFields) 
+			&& count($relationTableMatchFields) > 0) {
+				$relationMatchFields = array_merge($relationTableMatchFields, $relationMatchFields);
+		}
+			// support for "tablenames" column
+		if ($columnMap->getRelationTableRelatedTableColumnName() !== NULL) {
+			$relationMatchFields[$columnMap->getRelationTableRelatedTableColumnName()] = $dataMap->getTableName();
+		}
+	}
+
+	/**
 	 * Iterate over deleted aggregate root objects and process them
 	 *
 	 * @return void
Index: Classes/Persistence/Mapper/ColumnMap.php
===================================================================
--- Classes/Persistence/Mapper/ColumnMap.php	(revision 3926)
+++ Classes/Persistence/Mapper/ColumnMap.php	(working copy)
@@ -120,6 +120,20 @@
 	protected $relationTablePageIdColumnName;
 
 	/**
+	 * Flag if the current relation is a multiColumn relation
+	 *
+	 * @var boolean
+	 **/
+	protected $isMultiColumnRelation;
+
+	/**
+	 * The name of the column of the relation table holding the name of the related table
+	 *
+	 * @var string
+	 **/
+	protected $relationTableRelatedTableColumnName;
+
+	/**
 	 * An array of field => value pairs to both insert and match against when writing/reading MM relations
 	 *
 	 * @var array
@@ -238,6 +252,26 @@
 		return $this->relationTablePageIdColumnName;
 	}
 
+	public function setRelationTableRelatedTableColumnName($relationTableRelatedTableColumnName) {
+		$this->relationTableRelatedTableColumnName = $relationTableRelatedTableColumnName;
+	}
+
+	public function getRelationTableRelatedTableColumnName() {
+		return $this->relationTableRelatedTableColumnName;
+	}
+
+	public function setIsMultiColumnRelation($isMultiColumnRelation) {
+		$this->isMultiColumnRelation = (boolean) $isMultiColumnRelation;
+	}
+
+	public function getIsMultiColumnRelation() {
+		return $this->isMultiColumnRelation;
+	}
+
+	public function isMultiColumnRelation() {
+		return self::getIsMultiColumnRelation();
+	}
+
 	public function setRelationTableMatchFields(array $relationTableMatchFields) {
 		$this->relationTableMatchFields = $relationTableMatchFields;
 	}
Index: Classes/Persistence/Mapper/DataMapFactory.php
===================================================================
--- Classes/Persistence/Mapper/DataMapFactory.php	(revision 3926)
+++ Classes/Persistence/Mapper/DataMapFactory.php	(working copy)
@@ -188,7 +188,7 @@
 	 * @return void
 	 */
 	protected function setRelations(Tx_Extbase_Persistence_Mapper_ColumnMap $columnMap, $columnConfiguration, $propertyMetaData) {
-		if (isset($columnConfiguration)) {
+		if (isset($columnConfiguration) && $this->isSupportedRelationConfiguration($columnConfiguration, $propertyMetaData)) {
 			if (isset($columnConfiguration['MM']) || isset($columnConfiguration['foreign_selector'])) {
 				$columnMap = $this->setManyToManyRelation($columnMap, $columnConfiguration);
 			} elseif (isset($propertyMetaData['elementType'])) {
@@ -214,11 +214,15 @@
 	 */
 	protected function setOneToOneRelation(Tx_Extbase_Persistence_Mapper_ColumnMap $columnMap, $columnConfiguration) {
 		$columnMap->setTypeOfRelation(Tx_Extbase_Persistence_Mapper_ColumnMap::RELATION_HAS_ONE);
-		$columnMap->setChildTableName($columnConfiguration['foreign_table']);
+		$columnMap->setChildTableName($this->resolveDefaultChildTableName($columnConfiguration));
 		$columnMap->setChildTableWhereStatement($columnConfiguration['foreign_table_where']);
-		$columnMap->setChildSortbyFieldName($columnConfiguration['foreign_sortby']);
-		$columnMap->setParentKeyFieldName($columnConfiguration['foreign_field']);
-		$columnMap->setParentTableFieldName($columnConfiguration['foreign_table_field']);
+
+		if($columnConfiguration['type'] != 'group') {
+			$columnMap->setChildKeyFieldName($columnConfiguration['foreign_key_field']);
+			$columnMap->setChildSortbyFieldName($columnConfiguration['foreign_sortby']);
+			$columnMap->setParentKeyFieldName($columnConfiguration['foreign_field']);
+			$columnMap->setParentTableFieldName($columnConfiguration['foreign_table_field']);
+		}
 		return $columnMap;
 	}
 
@@ -232,11 +236,15 @@
 	 */
 	protected function setOneToManyRelation(Tx_Extbase_Persistence_Mapper_ColumnMap $columnMap, $columnConfiguration) {
 		$columnMap->setTypeOfRelation(Tx_Extbase_Persistence_Mapper_ColumnMap::RELATION_HAS_MANY);
-		$columnMap->setChildTableName($columnConfiguration['foreign_table']);
+		$columnMap->setChildTableName($this->resolveDefaultChildTableName($columnConfiguration));
 		$columnMap->setChildTableWhereStatement($columnConfiguration['foreign_table_where']);
-		$columnMap->setChildSortbyFieldName($columnConfiguration['foreign_sortby']);
-		$columnMap->setParentKeyFieldName($columnConfiguration['foreign_field']);
-		$columnMap->setParentTableFieldName($columnConfiguration['foreign_table_field']);
+
+		if($columnConfiguration['type'] != 'group') {
+			$columnMap->setChildKeyFieldName($columnConfiguration['foreign_key_field']);
+			$columnMap->setChildSortbyFieldName($columnConfiguration['foreign_sortby']);
+			$columnMap->setParentKeyFieldName($columnConfiguration['foreign_field']);
+			$columnMap->setParentTableFieldName($columnConfiguration['foreign_table_field']);
+		}
 		return $columnMap;
 	}
 
@@ -251,25 +259,58 @@
 	protected function setManyToManyRelation(Tx_Extbase_Persistence_Mapper_ColumnMap $columnMap, $columnConfiguration) {
 		$columnMap->setTypeOfRelation(Tx_Extbase_Persistence_Mapper_ColumnMap::RELATION_HAS_AND_BELONGS_TO_MANY);
 		if (isset($columnConfiguration['MM'])) {
-			$columnMap->setChildTableName($columnConfiguration['foreign_table']);
+			$foreignTable = $this->resolveDefaultChildTableName($columnConfiguration);
+
+			$columnMap->setChildTableName($foreignTable);
 			$columnMap->setChildTableWhereStatement($columnConfiguration['foreign_table_where']);
 			$columnMap->setRelationTableName($columnConfiguration['MM']);
-			if (is_array($columnConfiguration['MM_match_fields'])) {
-				$columnMap->setRelationTableMatchFields($columnConfiguration['MM_match_fields']);
+
+			$matchFields = is_array($columnConfiguration['MM_match_fields']) ? $columnConfiguration['MM_match_fields'] : array();
+			$insertFields = is_array($columnConfiguration['MM_insert_fields']) ? array_merge($matchFields, $columnConfiguration['MM_insert_fields']) : $matchFields;
+			if (count($matchFields)) {
+				$columnMap->setRelationTableMatchFields($matchFields);
 			}
-			if (is_array($columnConfiguration['MM_insert_fields'])) {
-				$columnMap->setRelationTableInsertFields($columnConfiguration['MM_insert_fields']);
+			if (count($insertFields)) {
+				$columnMap->setRelationTableInsertFields($insertFields);
 			}
+
 			$columnMap->setRelationTableWhereStatement($columnConfiguration['MM_table_where']);
+
+			$useRelationTableRelatedTableName = FALSE;
+
 			if (!empty($columnConfiguration['MM_opposite_field'])) {
 				$columnMap->setParentKeyFieldName('uid_foreign');
 				$columnMap->setChildKeyFieldName('uid_local');
 				$columnMap->setChildSortByFieldName('sorting_foreign');
+
+				$foreignTable = $this->resolveDefaultChildTableName($columnConfiguration);
+				$foreignTableDefinitions = $this->getColumnsDefinition($foreignTable);
+				$oppositeFieldConfiguration = $foreignTableDefinitions[$columnConfiguration['MM_opposite_field']];
+
+				// don't set the columnMap to multiColumnRelation here, because the relation itself is not treated as such
+				// all we need is to define the relationTableRelatedTableColumnName here in order to build the correct MM relations
+				if ($this->isMultiColumnRelation($oppositeFieldConfiguration)) {
+					$useRelationTableRelatedTableName = TRUE;
+				}
 			} else {
 				$columnMap->setParentKeyFieldName('uid_local');
 				$columnMap->setChildKeyFieldName('uid_foreign');
 				$columnMap->setChildSortByFieldName('sorting');
+				$columnMap->setIsMultiColumnRelation( $this->isMultiColumnRelation($columnConfiguration) );
 			}
+
+			// automatically set required 'tablenames' fields on the relation table, just like TYPO3 core does on certain MM relations
+			// @see function writeMM of class class.t3lib_loaddbgroup.php
+			if (($columnConfiguration['type'] === 'group' && $columnConfiguration['prepend_tname'])
+				|| $columnConfiguration['neg_foreign_table']) {
+					if (!isset($matchFields['tablenames'])) {
+						$useRelationTableRelatedTableName = TRUE;
+					}
+			}
+			if ($useRelationTableRelatedTableName === TRUE
+				|| $columnMap->isMultiColumnRelation() === TRUE) {
+					$columnMap->setRelationTableRelatedTableColumnName('tablenames');
+			}
 		} elseif (isset($columnConfiguration['foreign_selector'])) {
 			$columns = $this->getColumnsDefinition($columnConfiguration['foreign_table']);
 			$childKeyFieldName = $columnConfiguration['foreign_selector'];
@@ -287,4 +328,59 @@
 		return $columnMap;
 	}
 
+	/**
+	 * Checks if the given columnConfiguration belongs to a multiTable relation
+	 *
+	 * @param array $columnConfiguration The column configuration from $GLOBALS['TCA']
+	 * @return boolean
+	 * @see class.t3lib_loaddbgroup.php function readMM and writeMM
+	 */
+	private function isMultiColumnRelation($columnConfiguration) {
+		if ( is_array($columnConfiguration)
+			&& isset($columnConfiguration['allowed']) ) {
+				$allowedTables = t3lib_div::trimExplode(',', $columnConfiguration['allowed']);
+				if (count($allowedTables) > 1)	{
+					throw new Tx_Extbase_Persistence_Exception_UnsupportedRelation('Extbase currently doesn\'t support multiTable relations. You current TCA configuration tries to create a multiTable relation to these tables: ' . implode(', ', $tableNameArray), 1295571070);
+					#return TRUE;
+				}
+		}
+		return FALSE;
+	}
+
+	/**
+	 * Is resolving the correct childTableName from the given columnConfiguration.
+	 * The main purpose of this method is to return the default table name that should be used
+	 * to build the database relations in case it's a multitable relation like it's possible
+	 * with TCA type "group".
+	 *
+	 * @param array $columnConfiguration The column configuration from $GLOBALS['TCA']
+	 * @return string The name of the child table
+	 */
+	private function resolveDefaultChildTableName($columnConfiguration) {
+		$tableName = $columnConfiguration['allowed'] ? $columnConfiguration['allowed'] : $columnConfiguration['foreign_table'];
+		$tableNameArray = t3lib_div::trimExplode(',', $tableName);
+		if (count($tableNameArray) > 1) {
+			$tableName = current($tableNameArray);
+		}
+		return $tableName;
+	}
+
+	/**
+	 * Check is the given configuration matches supported relation configurations
+	 *
+	 * @param array $columnConfiguration The column configuration from  $GLOBALS['TCA']
+	 * @param array $propertyMetaData The property metadata as delivered by the reflection service
+	 * @return boolean
+	 */
+	private function isSupportedRelationConfiguration($columnConfiguration, $propertyMetaData) {
+		if (isset($columnConfiguration['foreign_table'])) {
+			return TRUE;	
+		}
+		if ($columnConfiguration['type'] == 'group'
+			&& $columnConfiguration['internal_type'] == 'db'
+			&& isset($columnConfiguration['allowed'])) {
+					return TRUE;
+		}
+		return FALSE;
+	}
 }
\ No newline at end of file
Index: Classes/Persistence/Mapper/DataMapper.php
===================================================================
--- Classes/Persistence/Mapper/DataMapper.php	(revision 3926)
+++ Classes/Persistence/Mapper/DataMapper.php	(working copy)
@@ -387,13 +387,14 @@
 	 * @return Tx_Extbase_Persistence_QOM_ConstraintInterface $constraint
 	 */
 	protected function getConstraint(Tx_Extbase_Persistence_QueryInterface $query, Tx_Extbase_DomainObject_DomainObjectInterface $parentObject, $propertyName, $fieldValue = '', $relationTableMatchFields = array()) {
-		$columnMap = $this->getDataMap(get_class($parentObject))->getColumnMap($propertyName);
+		$dataMap = $this->getDataMap(get_class($parentObject));
+		$columnMap = $dataMap->getColumnMap($propertyName);
 		if ($columnMap->getParentKeyFieldName() !== NULL) {
 			$constraint = $query->equals($columnMap->getParentKeyFieldName(), $parentObject);
  			if($columnMap->getParentTableFieldName() !== NULL) {
  				$constraint = $query->logicalAnd(
 					$constraint,
-					$query->equals($columnMap->getParentTableFieldName(), $this->getDataMap(get_class($parentObject))->getTableName())
+					$query->equals($columnMap->getParentTableFieldName(), $dataMap->getTableName())
 					);
  			}
 		} else {
@@ -404,6 +405,10 @@
 				$constraint = $query->logicalAnd($constraint, $query->equals($relationTableMatchFieldName, $relationTableMatchFieldValue));
 			}
 		}
+			// support for "tablenames" column
+		if ($columnMap->getRelationTableRelatedTableColumnName() !== NULL) {
+			$constraint = $query->logicalAnd($constraint, $query->equals($columnMap->getRelationTableRelatedTableColumnName(), $dataMap->getTableName()));
+		}
 		return $constraint;
 	}
 
Index: Classes/Persistence/Storage/Typo3DbBackend.php
===================================================================
--- Classes/Persistence/Storage/Typo3DbBackend.php	(revision 3926)
+++ Classes/Persistence/Storage/Typo3DbBackend.php	(working copy)
@@ -673,6 +673,17 @@
 			$sql['unions'][$relationTableName] = 'LEFT JOIN ' . $relationTableName . ' ON ' . $tableName . '.uid=' . $relationTableName . '.uid_local';
 			$sql['unions'][$childTableName] = 'LEFT JOIN ' . $childTableName . ' ON ' . $relationTableName . '.uid_foreign=' . $childTableName . '.uid';
 			$className = $this->dataMapper->getType($className, $propertyName);
+
+			$relationTableMatchFields = $columnMap->getRelationTableMatchFields();
+			if (is_array($relationTableMatchFields) && count($relationTableMatchFields)) {
+				foreach ($relationTableMatchFields as $matchFieldName => $matchFieldValue) {
+					$sql['unions'][$relationTableName] .= ' AND ' . $relationTableName . '.' . $matchFieldName . '=' . $this->databaseHandle->fullQuoteStr($matchFieldValue, 'foo');
+				}
+			}
+				// support for "tablenames" column
+			if ($columnMap->getRelationTableRelatedTableColumnName() !== NULL) {
+				$sql['unions'][$relationTableName] .= ' AND ' . $columnMap->getRelationTableRelatedTableColumnName() . '=' . $this->databaseHandle->fullQuoteStr($tableName, 'foo');
+			}
 		} else {
 			throw new Tx_Extbase_Persistence_Exception('Could not determine type of relation.', 1252502725);
 		}