Backbone Subset

gistfile1.txt

Backbone.Subset = Backbone.Collection.extend({
    superset: null,

    initialize: function(models, options){
      this.superset = options.superset || this.superset;
      this.sieve = options.sieve || this.sieve;

      if (!this.superset) throw new Error('Missing superset for Backbone.Subset');

      _.each(['add', 'remove', 'reset', 'change'], function(evt){
        this.superset.on(evt, this.setModels, this);
      }, this);

      this.setModels();
    },

    setModels: function(){
      this.set(this.superset.filter(this.sieve));
    },

    sieve: function(model){
      return true;
    }
  });

// Usage
var completedModels = new Backbone.Subset(null, {
    superset: App.models,

    sieve: function(model){
        return model.get('isCompleted');
    }
});