获取指向给定对象的所有Parse.Relations

Question

我正在使用a Parse.Relation在主题下对用户进行分组.如何检索topic.relation指向给定用户的所有主题？

问题是在单个调用/回调中执行此操作.

// 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

构造Topic类的查询,并添加equalTo约束.

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

这将返回在其朋友关系中包含用户的所有Topic对象.