Create sub-collections from other collections and keep them in sync
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.npmignore First commit Sep 13, 2012
backbone.collectionsubset.js Add backbone 0.9.9 support Dec 20, 2012


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Create sub-collections of other collections and keep them in sync. This library allows you create child collections that are subsets of larger collections based on a filter function. These children can then be further subset into even smaller collections. This creates a tree of collections with a single parent collection at the top. Adding a model to the root collection will automatically push the model down the tree and into subsets that match that model.

Each subset is its own independent collection. It can have its own URL for fetching which will add all the models to the parent collection and refilter the subset.

Imagine you have a collection of tasks. You can create a subset for "today". If you add a model to the parent collection it will be pushed into the "today" collection. You can further subset the "today" collection into subsets for assigned users.


  • Create subsets of large collections
  • Subsets are independent collections and can have their own URL and properties.
  • Subsets will be reset when the parent is reset
  • Adding a model to a parent pushes it down into all subsets it belongs to firing add events in each
  • Adding a model to a child pushes it up to the top which will then move in into matching subsets
  • Models in subsets point to the object


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: 200, today: 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

Getting Started


Download the production version or the development version.

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


bower install backbone.collectionsubset


npm install backbone.collectionsubset


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({
  filter: function(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,
  filter: function(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!

Release History

(Nothing yet)


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