private function createRelation($field, $relation)
    {
        switch ($relation) {
            case self::ONE_TO_ONE_RELATION:
                return new OneToOneRelation($field);
                break;

            case self::ONE_TO_MANY_RELATION:
                return new OneToManyRelation($field);
        }
    }
private function createRelation($field, $relation)
    {
        switch ($relation) {
            case self::ONE_TO_ONE_RELATION:
                return new OneToOneRelation($field);
                break;

            case self::ONE_TO_MANY_RELATION:
                return new OneToManyRelation($field);
        }
    }
@param string $field
@param string $relation

@return Relation