public static function addRelationship($query, $relationship)
    {
        $property = $query->getRepository()->getDescription()->getProperty($relationship);

        switch (true) {
            case $property->isManyToOne() :
                return self::_parseManyToOne($query, $property);
            case $property->isManyToMany() :
                return self::_parseManyToMany($query, $property);
            case $property->isOneToMany() :
                return self::_parseOneToMany($query, $property);

        }
    }