Find Collection from Model in Backbone

I'm changing state on a model view and I was wondering what would be a clean way to find out the collection the model is referenced from.

Essentially it works like this: when a model is triggered to turn 'on' it needs to first go up a level and have the collection query the other models and turn any that are currently 'on' to 'off'. Right now I'm passing each model view a reference to the collection view it comes from so it can query the collection from there, but I feel that might be bad practice.

Solution

From the fine manual:

Any event that is triggered on a model in a collection will also be triggered on the collection directly, for convenience.

So if you change an attribute, active, on a model in a collection, then both the model and the collection will trigger "change:active" events. You could have the collection listen to itself for the appropriate "change" events:

initialize: function() {
    _.bindAll(this, 'active_changed');
    this.on('change:active', this.active_changed);
},
active_changed: function(active_m) {
    if(!active_m.get('active'))
        return;
    this.each(function(m) {
        if(m.id != active_m.id) {
            console.log('Updating ' + m.id);
            m.set({ active: false }, { silent: true });
        }
    });
}

The {silent:true} on set is just there to avoid generating even more events from the internal bookkeeping; this may or may not be appropriate in your case.

Demo: http://jsfiddle.net/ambiguous/VAnUq/

Only having one model in the "on" state is a collection-level property so it makes sense for the collection to manage this for all of its models.