Simple way to get multiple related objects in Parse.com with Javascript?

Question

I have a Player class. Players can have x number of Trophies. I have the Player objectId and need to get a list of all of their Trophies.

In the Parse.com data browser, the Player object has a column labeled:

trophies Relation<Trophy>
(view Relations)

This seems like it should be so simple but I'm having issues with it.

I have the ParseObject 'player' in memory:

var query = new Parse.Query("Trophy");
query.equalTo("trophies", player);
query.find({
  /throws an error- find field has invalid type array.

I've also tried relational Queries:

var relation = new Parse.Relation(player, "trophies");
relation.query().find({
  //also throws an error- something about a Substring being required.

This has to be a completely common task, but I can't figure out the proper way to do this.

Anyone know how to do this in Javscript CloudCode?

Many thanks!

EDIT--

I can do relational queries on the user fine:

var user = Parse.User.current();
var relation = user.relation("trophies");
relation.query().find({

I don't understand why this very same bit of code breaks if I'm using a non-user object.

Answer 1

I finally sorted this out, though there is a caveat that makes this work differently than the documentation would indicate.

//Assuming we have 'player', an object of Class 'Player'.

var r = player.relation("trophies");
r.query().find({
  success: function(trophies){
    response.success(trophies); //list of trophies pointed to by that player's "trophies" column.
  },
  error: function(error){
    response.error(error);
  }

})

The caveat: You must have a 'full' player object in memory for this to work. You can't save a player object, grab the object from the success callback and have this work. Some reason, the object that is returned in the success handler is appears to be an incomplete Parse.Object, and is missing some of the methods required to do this.

Another stumbling block about the Parse.com Javascript SDK- A query that finds nothing is still considered successful. So every time you query for something, you must check the length of the response for greater than 0, because the successful query could have returned nothing.

Answer 2

This is what worked for me:

        var Comment = Parse.Object.extend("Comment");
        var commentsQuery = new Parse.Query(Comment);
        commentsQuery.equalTo("parent", video);//for the given 'video' instance, find its children (comments)
        commentsQuery.descending("createdAt");
        return commentsQuery.find();

Note: of course, video is an instance of the Video class. And returning find() means I'll have to handle the 'promise' in whatever function calls this one.

And here is another function coming from the other angle:

    getRecentCommentsOfAllVideos: function(limit) {
        var Comment = Parse.Object.extend("Comment");
        var commentsQuery = new Parse.Query(Comment);
        commentsQuery.descending("createdAt");
        commentsQuery.limit(limit);
        commentsQuery.include("parent");//this enables the details of the comment's associated video to be available in the result
        return commentsQuery.find();
    }

(Be sure to read https://parse.com/docs/js_guide and search for the line that says "Include the post data with each comment".)

I also looked at these materials; maybe they'll help you (though they weren't much help for me):

• https://parse.com/questions/how-to-retrieve-parent-objects-with-their-children-in-one-call-javascript-api
• http://blog.parse.com/2011/12/06/queries-for-relational-data/