Backbone Relational: relation lost during saving - backbone.js

Question

Today I updated backbone.js (0.9.2 => 0.9.9) and backbone-relational (0.5.0 => 0.7.0), and a piece of code stopped working and I can't figure our why. (I even tried to upgrade step by step (e.g. backbone-relational 0.5.0 => 0.6.0), but that didn't helped.)
My models (a book that contains several chapters):
window.Book = Backbone.RelationalModel.extend({
relations:[{
type: Backbone.HasMany,
key:"chapters",
relatedModel: "Chapter",
collectionType:"ChaptersCollection",
reverseRelation:{
key:"book"
}
}]
});
window.BookCollection = Backbone.Collection.extend({
model: Book,
url: "/books"
});
window.Chapter = Backbone.RelationalModel.extend();
window.ChaptersCollection = Backbone.Collection.extend({
model: Chapter,
url: "/chapters"
});
Now I want to add a chapter to an existing book, and do something during the "add" event. The problem is that chapter.get("book")is undefined, although the book is returned in the successcallback. But see yourself:
var book = ...;
book.get("chapters").on("add", function (chapter) {
console.log("add");
console.log(chapter.get("id"));
console.log(chapter.get("book_id"));
console.log(chapter.get("book"));
});
var chapter = book.get("chapters").create({title:"Foo"}, {
wait: true,
success:function () {
console.log("success")
console.log(chapter.get("id"));
console.log(chapter.get("book_id"));
console.log(chapter.get("book"));
}
});
Console output:
> add
> 83
> 3
> null <<<<<<< Expecting a book object here, why null?
> success
> 83
> 3
> Book{...}
Do you have any idea what I am doing wrong?

Answer 1

The issue seems to be that when the add event is fired for the child collection, the reverse relation hasn't yet been updated. I'm not sure what change in Backbone or Backbone.Relational between versions caused this change, but it's easy to fix.
Instead of listening to the add event on the related collection like you do here:
book.get("chapters").on("add", function (chapter) {
You should listen to the add:<key> event on the model itself as described in the Backbone.Relational documentation:
book.on("add:chapters", function (chapter) {
Check out this fiddle for a working example.