有没有办法按Parse中的关系对象的属性对查询进行排序？当我尝试按用户名排序时，它不会给我一个错误，但它也没有正确地对对象进行排序。
// Query for all friends the current user is following
var relationshipQuery: PFQuery = PFQuery(className: "Relationship")
relationshipQuery.whereKey("follower", equalTo: currentUser)
// Include the user
relationshipQuery.includeKey("followed")
// Order by username
relationshipQuery.orderByDescending("username")