Backbone.VirtualCollection allows you use display a subset of a backbone collection in a Backbone view that updates it real time. It works great with Marionette CollectionViews.
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 instantiate a virtual collection, that only contains tasks that belong to Rupert (who has user_id 13).
The constructor 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.
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 nameYou 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 changedThe 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
});It's very common that you'd want to update the filter being used, and have the collection view update itself. updateFilter takes the same paramters as the original filter property (a hash, or a function) and regenerates the virtual collection, without loosing your view bindings.
virtual_collection.updateFilter({
the_new: 'properties'
, are: 'lovely'
});
// or
virtual_collection.updateFilter(function (model) {
return model.foo() === 'bar';
});VirtualCollection does not store, or duplicate any data. We've used other solutions in the past, and duplicating data is just plain bad news.
VirtualCollection maintains an internal index of models that pass the filter. That way using the accesors, and iteraters (map, each, etc) is fast. It doesn't have to go through the whole parent collection and re-evaluate the all the filters.
By the way,
VirtualCollection.buildFilterFromHashis the function that turns a object into a filter function.You might find it usefull.
Happy hacking!
0.4.15 Added virtual_collection.model (via @fcsonline)
0.4.14 Added Backbone.extend (via @enov)
0.4.13 Optimized `_models` and `get` to access parent collections which are indexed
0.4.12 Pass the correct index in options object on model removal
0.4.11 Trigger `reset` in updateFilter (fixes issue with multilayer filtering)
0.4.10 Added Bower support
0.4.9 Added `where` and `findWhere`. Renamed internal filterFunction
0.4.8 Add `add` and `remove` proxies. Add index argument to filter function.
0.4.7 Add the updateFilter method (via @justinwinslow)
0.4.6 Add toJSON method (via @gbedardsice)
0.4.5 Add close_with option
0.4.4 Add all collection Underscore iterator proxies
0.4.3 Fix bug with onChange handler not proxying 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 unbinding of index listeners
0.2.0 Use cid instead of ids
0.1.1 Fixed issues with comparators specified as a function
0.1.0 Added support for comparators & sorting, separate from the parent collection
0.0.2 Fix buildFilterFromHash not detecting null values
- discuss/edit/merge PR's
npm version patch- update changelog in README.md
- update version number in component.json, bower.json
git push && git push --tags
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