/**
  * Builds the DDL SQL for a ForeignKey object.
  *
  * @param ForeignKey $fk
  *
  * @return string
  */
 public function getForeignKeyDDL(ForeignKey $fk)
 {
     if ($this->supportsForeignKeys($fk->getTable())) {
         return parent::getForeignKeyDDL($fk);
     }
     return '';
 }