src/bundles/Database/Model.php
protected function has_one( $model, $foreign_key = null, $local_key = null )
	{
		return new Model_Relation_HasOne( $this, $model, $foreign_key, $local_key );
	}
protected function has_one( $model, $foreign_key = null, $local_key = null )
	{
		return new Model_Relation_HasOne( $this, $model, $foreign_key, $local_key );
	}
protected function has_one ( $ model , $ foreign_key = null , $ local_key = null ) { return new Model_Relation_HasOne ( $ this , $ model , $ foreign_key , $ local_key ) ; }
Has one releationships

Model Car:
function engine()
{
return $this->has_one( 'Car_Engine', 'car_id', 'id' );
}

@param Model			$model
@param mixed			$foreign_key
@param mixed			$key
@return array
Has one releationships