public function delete($entity) {
	$identifier = $this->_em->getUnitOfWork()->getEntityIdentifier($entity);
        $this->deleteJoinTableRecords($identifier);

        $id = array_combine($this->_class->getIdentifierColumnNames(), $identifier);
        $this->_conn->delete($this->_class->getQuotedTableName($this->_platform), $id);
}

        $id = array_combine($this->_class->getIdentifierColumnNames(), $identifier);
        // might be fixed in this way (as example):
        foreach ($identifier as $columnName => $value) {
                $id[$this->_class->getQuotedColumnName($columnName, $this->_platform)] = $value;
        }