Parse Cloud Code: Modify Object before Retrieval - parse-platform

Question

Let's say I have a Users class and a Posts class, and each Post object has a User pointer. I also have a Comment class, and each Comment has a User pointer. Whenever I fetch a User, I want to fetch all the Posts and Comments that user has made in one network query. Compounding sub-queries won't work, since I have multiple data types. Ideally, I would like to have the Posts and Comments be properties of the retrieved User object.
Is there a way, in Cloud Code, to intercept object requests and modify them to have the appropriate properties before sending to the client?

Answer 1

You can't modify an object on retrieval, but you can write your own Cloud Function. In your Cloud Function you could take the ID of a user as a parameter, then create a composite object by combining the output of your 3 queries into one result.
You'll need to query:
User object
Posts for that user
Comments for that user
You could get the promise for each of those queries (find() etc return a promise object) and use Parse.Promise.when(userQueryPromise, postQueryPromise commentQueryPromise) to build your composite object and return it.
var _ = require('underscore');
Parse.Cloud.define('getUserWithPostsAndComments', function(request, response) {
var userId = request.params.userId;
var userPointer = new Parse.User();
userPointer.id = userId;
var userQuery = new Parse.Query(Parse.User);
var postQuery = new Parse.Query('Post');
postQuery.equalTo('user', userPointer);
var commentQuery = new Parse.Query('Comment');
commentQuery.equalTo('user', userPointer);
Parse.Promise.when(userQuery.get(userId), postQuery.find(), commentQuery.find())
.then(function(user, posts, comments) {
var composite = {
// User properties you want
name: user.get('username'),
email: user.get('email')
};
// Post properties you want
composite.posts = _.map(posts, function(post) {
return {
id: post.id,
title: post.get('title')
};
});
// Comment properties you want
composite.comments = _.map(comments, function(comment) {
return {
id: comment.id,
body: comment.get('bodyText')
};
});
// return the composite object
response.success(composite);
}, function(error) {
response.error(error);
});
});
Alternatively the above then block could just return the raw results, e.g.:
.then(function(user, posts, comments) {
return {
user: user,
posts: posts,
comments: comments
};
}, function(error) {
// etc...