Create relation between two classes to allow data query

To create a one-to-many relationship there are a couple of options:

• Use "back reference" links, i.e. add a friendRequest pointer to your myBadges class (only supports one-to-many)
• Add a column of type Array (good for small lists, supports many-to-many)
• Add a column of type Relation (use queries to navigate, supports many-to-many)
• Create a custom class to hold the relationships (if you have other data about each join, supports many-to-many) The simplest option is using the Array column, in JavaScript you just use a normal array that contains myBadges instances and assign it to a property of your parent class.

Note: In my examples below, I'm going to change the case of call classes to UpperCamel singular (myBadges -> MyBadge) and all properties/column names to lowerCamel (BadgeName -> badgeName) for consistency, and I suggest you do the same.

Examples:

Common code assumed in the below:

var FriendRequest = Parse.Object.extend("FriendRequest");
var MyBadge = Parse.Object.extend("MyBadge");
var friendRequest = /* some FriendRequest you've loaded */

Option 1 - back-reference

Adding new badge to a friend request:

// MyBadge.friendRequest: Pointer (to FriendRequest)
var myBadge = new MyBadge();
myBadge.set({
    badgeName: someStringVariable,
    uploadedBy: someUserObject,
    friendRequest: friendRequest
});
myBadge.save();

Getting badges for a friend request:

var badgesQuery = new Parse.Query(MyBadge);
badgesQuery.equalTo('friendRequest', friendRequest);
badgesQuery.find({
    success: function(badges) {
        // use badges as needed...
    }
});

Showing MyBadge rows for FriendRequest parent in Data Browser:

Get the objectId of a FriendRequest row, then on the view for MyBadge add a filter on the friendRequest column and paste the ID.

Option 2 - Array

Adding new badge to a friend request:

// FriendRequest.badges: Array (of MyBadge)

// 2-step process, first create and save the MyBadge instance
var myBadge = new MyBadge();
myBadge.set({
    badgeName: someStringVariable,
    uploadedBy: someUserObject
});
myBadge.save()
// step 2 (using chaining here) attach the saved badge to the friend request
.then(function() {
    friendRequest.badges.addUnique(myBadge);
    // return promise to allow further chaining
    return friendRequest.save();
});

Getting badges for a friend request:

// just include them when querying for FriendRequest objects
friendRequestQuery.include('badges');

Showing MyBadge rows for FriendRequest parent in Data Browser:

No support for this, you'll need to create your own solution.

Option 3 - Relation

Adding new badge:

// FriendRequest.badges: Relation (of MyBadge)

// 2-step process, first create and save the MyBadge instance
var myBadge = new MyBadge();
myBadge.set({
    badgeName: someStringVariable,
    uploadedBy: someUserObject
});
myBadge.save()
// step 2 (using chaining here) attach the saved badge to the friend request
.then(function() {
    var badgesRelation = friendRequest.relation('badges');
    badgesRelation.add(myBadge);
    // return promise to allow further chaining
    return friendRequest.save();
});

Getting badges for a friend request:

// query the relation
var badgesRelation = friendRequest.relation('badges');
var badgesQuery = badgesRelation.query();
// apply any filters as you would for any normal Parse.Query()
// ...
// use find() or any other query method
badgesQuery.find({
    success: function(badges) {
        // use array of badges...
    }
})

Showing MyBadge rows for FriendRequest parent in Data Browser:

Double-click on a value in the badges column.

Option 4 - custom join class

This isn't really suitable for your use-case, so I'm not going to provide a sample here.