Christopher DuBois Christopher DuBois - 4 months ago 18
Javascript Question

Creating nested models in Backbone with Backbone-relational

I would like to use backbone-relational to have nested models in my backbone.js application.

I have been able to follow the examples in the documentation to create nested objects (e.g. one-to-many relations). However I don't understand how to bind the lower level elements in a way that will update the upper level objects. I think a working application would be a very helpful tutorial.

So my question is: How do I extend the Todos tutorial using

so that:

  • one can add/remove subitems for each item

  • double clicking on any subitem edits it (just like the original Todo example)

  • clicking on an item hides/reveals its subitems

  • subitems are not fetched separately but are simply an array attribute of Todo items

Update: I have created a jsfiddle for this question. So far I have:

  • Imported the Todo example mentioned above

  • Created a
    model and a

  • Altered the
    model to extend
    instead of
    , with a
    relation to

  • Added a
    in the html code

But I'm still not sure how to:

  • add an input field for
    that appears only when you click a

  • have subitem data as an attribute of
    objects, but still have
    bind DOM elements to them (e.g.


I don't think I'd create a separate 'TodoSubItem' in this case - why not create a HasMany relation from Todo->Todo, so a Todo can have 0..* children, and 0..1 parent?

This way, you can re-use the order logic (if you change it to apply per collection), can create deeper nesting levels as desired (or limit that to a certain depth, if you want as well), etc. A number of things will need to be updated though, to accomodate this - for example, keep a list of child views so you can loop over them to mark each as done, and maintaining (and updating from) an ordering per TodoList.

Anyway, a rough outline of a possible solution to get you started, as a sort of diff with your current version (sorry, it's completely untested and could thus contain horrible mistakes):

//Our basic **Todo** model has `text`, `order`, and `done` attributes.
window.Todo = Backbone.RelationalModel.extend({

    relations: [{
        type: Backbone.HasMany,
        key: 'children',
        relatedModel: 'Todo',
        collectionType: 'TodoList',
        reverseRelation: {
            key: 'parent',
            includeInJSON: 'id'

    initialize: function() {
        if ( !this.get('order') && this.get( 'parent' ) ) {
            this.set( { order: this.get( 'parent' ).nextChildIndex() } );

    // Default attributes for a todo item.
    defaults: function() {
        return { done: false };

    // Toggle the `done` state of this todo item.
    toggle: function() {{done: !this.get("done")});

    nextChildIndex: function() {
        var children = this.get( 'children' );
        return children && children.length || 0;

// The DOM element for a todo item...
window.TodoView = Backbone.View.extend({

    //... is a list tag.
    tagName:  "li",

    // Cache the template function for a single item.
    template: _.template($('#item-template').html()),

    // The DOM events specific to an item.
    events: {
        'click': 'toggleChildren',
        'keypress input.add-child': 'addChild',
        "click .check"              : "toggleDone",
        "dblclick div.todo-text"    : "edit",
        "click span.todo-destroy"   : "clear",
        "keypress .todo-input"      : "updateOnEnter"

    // The TodoView listens for changes to its model, re-rendering.
    initialize: function() {
        this.model.bind('change', this.render, this);
        this.model.bind('destroy', this.remove, this);

        this.model.bind( 'update:children', this.renderChild );
        this.model.bind( 'add:children', this.renderChild );

        this.el = $( this.el );

        this.childViews = {};

    // Re-render the contents of the todo item.
    render: function() {

        // Might want to add this to the template of course
        this.el.append( '<ul>', { 'class': 'children' } ).append( '<input>', { type: 'text', 'class': 'add-child' } );

        _.each( this.get( 'children' ), function( child ) {
            this.renderChild( child );
        }, this );

        return this;

    addChild: function( text) {
        if ( e.keyCode == 13 ) {
            var text = this.el.find( 'input.add-child' ).text();
            var child = new Todo( { parent: this.model, text: text } );

    renderChild: function( model ) {
        var childView = new TodoView( { model: model } );
        this.childViews[ model.cid ] = childView;
        this.el.find( 'ul.children' ).append( childView.render() );

    toggleChildren: function() {
        $(this.el).find( 'ul.children' ).toggle();

    // Toggle the `"done"` state of the model.
    toggleDone: function() {
        _.each( this.childViews, function( child ) {

    clear: function() {
        this.model.set( { parent: null } );

    // And so on...