Get data from 2nd level pointer in Parse

Question

I have a setup with Three relevant classes: _User, Article, and Profile. In Article I have a pointer named author for _User, and in Profile, I have the same; a pointer, but named user, for _User.

Now, I want to retrieve data from Article, with the cols firstname and lastname in Profile, where the pointer in Article matches the objectId in _User, and the pointer in Profile.

Basically what I would solve with an inner join in SQL.

How do I go about this with just one parse call?

This is what I have so far:

var Article = Parse.Object.extend("Article");
var query = new Parse.Query(Article);
query.include("category");
query.find({
  success: function(results) {
    console.log("Successfully retrieved " + results.length + " article(s):");
    // Do something with the returned Parse.Object values
    for (var i = 0; i < results.length; i++) {
      var object = results[i];
      console.log(object.get('title'));
      console.log(object.get('content'));
      console.log(object.get('category').get("categoryName"));
    }
  },
  error: function(error) {
    console.log("Error: " + error.code + " " + error.message);
  }
});

danh · Accepted Answer · 2015-08-04 17:20:45Z

2

Its a pleasure answering questions where the OP took the trouble to include a complete (and minimal) description of the data and the desired result.

I think I understand that you want to get Articles, and for each you want to get Profiles, and that the Profiles and articles are (logically) joined via a common pointer to User.

This can be done using an additional query per article. For clarity and maintainability, I like to break these things up into short, logical promise-returning functions, so...

// for handy array functions, like _.map, and turning var args into simple arrays
var _ = require('underscore');
// note: include underscore this way in cloud code (nodejs)
// for browser, see underscorejs.org to add to your project

// this will answer a promise that is fulfilled with an array of the form:
// [ { article:article_object, profile:profile_object }, {...}, ...]
function articlesWithProfiles() {
    var query = new Parse.Query("Article");
    query.include("category");
    query.include("author");
    return query.find().then(function(articles) {
        var promises = _.map(articles, function(article) {
            return profileForArticle(article);
        });
        return Parse.Promise.when(promises);
    });
}

// return a promise that's fulfilled by associating the given article with it's profile
function profileForArticle(article) {   
    var author = article.get("author");
    var query = new Parse.Query("Profile");
    query.equalTo("user", author);
    return query.first().then(function(profile) {
        return { article:article, profile:profile };
    });
}

// call it like this
articlesWithProfiles().then(function() {
    // see edit below
    var result = _.toArray(arguments);
    console.log(JSON.stringify(result));
}, function(error) {
    // handle error
    console.log(JSON.stringify(error));
});

edited Aug 4, 2015 at 17:20

answered Aug 3, 2015 at 20:49

danh

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10 Comments

Brian Emilius Over a year ago

Hmmm... Your snippet makes sense to me, but I can't seem to make it work - and it's something else that I am not qualified to guess. I've included underscore.js in my HTML, but I get this error: Uncaught ReferenceError: require is not defined EDIT: Oh wait, this is node.js? I'm not writing in node.js... How would I do _.map and _.toArray without underscore.js?

danh Over a year ago

Require is how you use it in nodejs. To use it in your web app, get the source from (underscorejs.org which will lead you to github.com/jashkenas/underscore) and include it in your app with a <script> tag.

Brian Emilius Over a year ago

Yup, that's what I did as well, and included the underscore.js file in my HTML. But now I get this: Uncaught TypeError: Cannot read property 'then' of undefined <-- which is on the line after //call it like this

danh Over a year ago

Well that's just a convenience library. Should I add code to do those couple of functions natively?

Brian Emilius Over a year ago

If it isn't too much trouble, I would sorely appreciate it :)

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