获取指向给定对象的所有Parse.Relations

Question

我正在使用Parse.Relation将用户分组到一个主题下。如何检索具有指向给定用户的topic.relation的所有主题？

问题是如何在单个调用/回调中做到这一点。

// first add() a User object to the Topic's Parse.Relation
this.friendRelation = this.topic.relation("friend");
this.friendRelation.add(user);
// save the Topic to save its newly added .relation to Parse/Mongo
this.topic.save();

// iterate by adding the same User to several Topics

// (...)

// then you want to retrieve all Parse.Relations of all Topics where that 
// specific user is pointed to

// the non-optimized way is to traverse every row in the Topics index 
// and query each topic for its relations to find matching pointers to our user, 
// which means that the number of calls is bound to the number of rows – fine for
// 10 topics in Mongo but passed 100 it won't be tolerable.

Answer 1

为Topic类构造一个查询，并添加一个equalTo约束。

var query = new Parse.Query(Topic);
query.equalTo("friend", user);
query.find({success: function (returnedTopics) {
    ...
    },
    error: function (...) {
    }
});

这将返回所有在其好友关系中包含user的Topic对象。