Create sub-collections of other collections and keep them in sync


Create sub-collections of other collections and keep them in sync.

tasks = new TaskCollection
# Create a subset of our main collection 
today = tasks.subcollection
  filter: (task) -> task.isToday()
today.url = '/tasks/today'
# Create a new task in the main collection... 
tasks.create id: 200today: true
# ...and it's automatically pushed to all subsets 
today.get(200) is tasks.get(200) # true 
# Model changes are pushed upwards 
# Create models in subsets and they are pushed to the parent collection 
today.create id: 201
today.get(201) is tasks.get(2001) # true 
# And they will update on fetch 
# When subsets are fetched, all the models are pushed to the parent collection 

Download the production version or the development version.

In your web page:

<script src="dist/backbone.collectionsubset.min.js"></script>

Now you have two methods for creating subsets (or subcollections).

The easiest way to create a subset is to use Collection::subcollection

var TaskCollection = Backbone.Collection.extend();
var tasks = new TaskCollection;
var today = tasks.subcollection({
  filterfunction(task) {
    return task.isToday();

today will be an instance of tasks.constructor, in this case, TaskCollection.

If you need access to the subset object itself (you might want to modify the filter) you can create a subset directly.

var allTasks = new Backbone.Collection;
var subset = new Backbone.CollectionSubset({
  parent: allTasks,
  filterfunction(task) {
    return task.isToday();
var todayTasks = subset.child;
  return task.isYesterday();

Depending on how you create the subset you have different interface. Creating a subcollection via Backbone.Collection::subcollection you will only have access to the child collection and the Backbone.CollectionSubset instance is completely transparent. However, you may need some extra flexibility so you can also create Backbone.CollectionSubset instances manually

subset = new Backbone.CollectionSubet parent: tasks


new_collection = tasks.subcollection
  filter: (model) -> model.isToday()
  • refresh - Whether to refresh the collection from the parent immediately. Defaults to true
  • triggers - Set which model attribute changes to watch for. This is important for performance. Defaults to null
  • filter - The default filter. By default lets all models pass
  • child - The collection to use for the child. This isn't required and will be automatically created. Defaults to null
  • parent - required The collection to base the subset on. Must be a Backbone.Collection.

If you create a Backbone.CollectionSubset instance directly you will have access to these methods.


Set the parent collection. Will unbind any events on the collection that the subset current has and setup all the events for syncing with the child collection


Same as the previous option, but with the child collection.


Set the filter used on the parent collection. This does not automatically refresh the child collection.


Refreshes the child collection with models from the parent. Clears out the child collection and refilters the parent. Triggers a 'refresh' event on the child.


Clean up the subset. Removes the child collection completely and removes all events from the parent child. Triggers a dispose event on the subset.

  • Add url option to subcollection that will prepend the parent collection url

In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code using grunt.

Also, please don't edit files in the "dist" subdirectory as they are generated via grunt. You'll find source code in the "lib" subdirectory!

(Nothing yet)

Copyright (c) 2012 Anthony Short Licensed under the MIT license.