Backbone.VirtualCollection: A JavaScript repository from gbedardsice

Backbone.VirtualCollection

Backbone.VirtualCollection allows you use Backbone.Marionette CollectionViews and CompositeViews on a subset of a backbone collection.

Usage

For example, let's say you have a task collection, and want to show a list of tasks that belong to a specific user.

We can instanciate a virtual collection, that only contains tasks that belong to Rupert (who has user_id 13). The contructor takes two parameters, the first is the parent collection, the second is a options object. The filter option specifies a function that takes the model as argument. You can also just specify a hash of attributes to match.

var virtual_collection = new Backbone.VirtualCollection(tasks_collection, {
  filter: function (task) {
    return task.get('user_id') == 13;
  }
});
// or using a hash of attributes to match
virtual_collection = new Backbone.VirtualCollection(tasks_collection, {
  filter: {
    user_id: 13
  }
});

var view = new TaskListView({
  collection: virtual_collection
});

The marionette collection view will only display the tasks that belong to Rupert, and it will update automatically. In other words, when a task is created that belongs to Rupert it will appear, but not if it belongs to Bob.

Sorting

Be default, the virtual collection will have the same sorting order as the parent collection. However, a comparator can be specified to change this. The comparator behaves like a Backbone comparator. In other words, you can specify a function or the name of an attribute to sort by.

var virtual_collection = new Backbone.VirtualCollection(tasks_collection, {
  filter: { user_id: 13 },
  comparator: 'name'}
});
// tasks in the virtual_collection will be sorted by name

You can also change the sorting order on the fly.

virtual_collection.comparator = 'created_at';
virtual_collection.sort(); // triggers sort event
// virtual_collection is now sorted by date, but the parent collection has not changed

Unbinding

The virtual collection will keep listening to it's parent collection until you call stopListening.

You can use the helper function virtual_collection.closeWith to tell the collection to stopListening when a marionette view is closed.

var virtual_collection = new Backbone.VirtualCollection(collection, {filter: {foo: 'bar'}});
var view = new Marionette.CollectionView({collection: virtual_collection});
virtual_collection.closeWith(view);

Using the helper will take care of unbinding the virtual collection's listeners when the view is closed.

You also can pass a close_with option when creating the virtual collection being that an event emitter. The virtual collection will stop listening events when the close_with event emitter emits a close event.

var virtual_collection = new Backbone.VirtualCollection(collection, {
  filter: {foo: 'bar'},
  close_with: view
});

Philosophy

It's really light

VirtualCollection only implements the methods used by a Marionette CollectionView to render a collection. It does not attempt to mimic all the behaviours of an actual collection. This keeps the overhead down.

It's DRY

VirtualCollection does not store, or duplicate any data. We've used other solutions in the past, and duplicating data is just plain bad news.

It's Fast

VirtualCollection builds an internal index of model ids that pass the filter. That way iterating with the each, or map interator is fast. It doesn't have to go through the whole parent collection and re-evaluate the all the filters.

By the way, VirtualCollection.buildFilterFromHash is the function that turns a object into a filter function.You might find it usefull.

Happy hacking!

Changelog

0.4.5  Add close_with option
0.4.4  Add all collection Underscore interator proxies
0.4.3  Fix bug with onChange handler not proxing add and remove events correctly
0.4.2  Improve importing with npm
0.4.0  Make filter part of options hash. This version breaks backwards compatibility. You'll have to update your code.

0.3.3  Fix sort comparator with two args. Add more iterator helper functions
0.3.2  Fix reset event on parent collection
0.3.1  Replace viewHelper with closeWith
0.3.0  Fix undinbing of index listeners

0.2.0  Use cid instead of ids

0.1.1  Fixed issues with comparators specfied as a function
0.1.0  Added support for comparators & sorting, seperate from the parent collection
0.0.2  Fix buildFilterFromHash not detecting null values

License

The MIT License (MIT)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

gbedardsice/Backbone.VirtualCollection