/**
  * @param DatabaseSequence $sequence
  */
 public function addDatabaseSequence(DatabaseSequence $sequence)
 {
     // check to make sure the database isn't already assigned
     foreach ($this->database_sequences as $database_sequence) {
         if ($database_sequence->getDatabase()->getId() == $sequence->getDatabase()->getId()) {
             return null;
             // don't add it
         }
     }
     $sequence->setSubcategory($this);
     $sequence->setOwner($this->owner);
     $this->database_sequences[] = $sequence;
 }