Implements an imaginary subset of a Backbone Collection (as superset)

Backbone.Subset.js

/*
  @date   05/31/2011
  @class  Backbone.Subset
  @name   Backbone Subset
  @desc
    Implements an imaginary subset of a Backbone Collection (as superset)
*/  


// Extend the default Backbone.Collection

_.extend(Backbone.Collection.prototype, {
    
    build: function (attrs) {
        var model = new this.model(attrs);
        this.add(model);
        return model;
    },
    merge: function (collection) {
        this.add(collection.models);
        return this
    }
});


// Standard Constructor
Backbone.Subset = function(options) {


  this.options = options || (options={});

  // use the comparator supplied by the options
  if(options.comparator) {
    this.comparator = options.comparator;
    delete options.comparator;
  }

  if(!options.superset) { throw 'Subset must belong to a superset!'; }
  if(!options.filter) { throw 'Subset must have a filter'; }
  if(!(options.superset instanceof Backbone.Collection) && !(options.superset instanceof Backbone.Subset)) {
    throw "Subset must have Backbone.Collection or Backbone.Subset as its superset!";
  }

  var self = this;

  // transform method, to be applied on models
  this.transform  = options.transform || function(echo) { return echo; };
  this.filter     = options.filter;
  this.superset   = options.superset;

  // hook on superset's events
  this.superset.bind("all", function(ev) {
 
 	// TODO: CLEAN UP RESET!!!
 
	switch(ev) {
		case "add":
		case "remove":
			if(self.filter(arguments[1])) {
				// we are affected, forward events on this subset
    		self._reset();
				self.trigger.apply(self, arguments);
			}
			break;
		case "refresh":
			self._reset();
			break;
		default:
			// model has changed, maybe it doesn't belong in this subset anymore
			if(ev.indexOf("change:") === 0) {

				// sub collection already has object so it could be removed
				if(self.getByCid(arguments[1])) {
					// maybe trigger remove
					if(!self.filter(arguments[1])) {
						self._reset();
						self.trigger('remove', arguments[1], self);
					}
					else
					{
						// still in the set, forward event to this subset
						self._reset();
						self.trigger.apply(self, arguments);
					}
				}
				
				// we got a new element, yay!
				if(!self.getByCid(arguments[1]) && self.filter(arguments[1])) {
					self._reset();
					self.trigger('add', arguments[1], self);
				} 
			}
		
	}

  });

  // remove crucial entries from options
  delete options.filter
  delete options.superset;

  // get an event if a model changes
  this._boundOnModelEvent = _.bind(this._onModelEvent, this);

  // refresh the models
  this._reset();

  // call custom constructor
  this.initialize(options);
};




_.extend(Backbone.Subset.prototype, Backbone.Collection.prototype, {

  // array holding the models as json objects
  toJSON: function() {
    return this.map(function(c) {
      return c.toJSON();
    })
  },

  // add models
  add: function(models, options) {
  	
  	var self = this;
  	
  	models = _.filter(models, this.filter);
  	
  	// return if no models resist
  	if(models.length == 0) { return; }
  	
    // actually add the models to the superset
    this.superset.add(models, options);
    return this;
  },

  // remove models
  remove: function(models, options) {
    // remove model from superset
    this.superset.remove(_.filter(_.filter(models, function(cm) {
      return m != null;
    }), this.filter), options);
  },

  // get a certain model by id!
  get: function(model_id) {
    return _.select(this.models, function(cm) {
      return cm.id == model_id;
    })[0]
  },

  // get a certain model by cid !
  getByCid: function(model_cid) {
    return _.select(this.models, function(cm) {
      return cm.cid == (model_cid.cid || model_cid);
    })[0]
  },

  // get a model at a certain position in the _subset_
  at: function(index) {
    return this.models[index]
  },

  // sorting
  sort: function(options) {
    this.superset.sort(options);
    return this;
  },

  // pluck an attribute from each model in the subset
  pluck: function(attr) {
    return _.map(this.models, function(model) {
      return model.get(m)
    })
  },

  // refresh the superset (triggers event to refresh this one too)
  refresh: function(models, options) {
    this.superset.refresh(models, options);
    return this;
  },

  fetch: function(options) {
    this.superset.fetch(options);
    return this;
  },
  
  create: function(model, options) {
    return this.superset.create(model, options);
  },

  parse: function(resp) {
    return resp;
  },

  length: function() {
    this._reset();
    return this.models.length;
  },

  chain: function() {
    return this.superset.chain();
  },

  // reset state and refresh the models
  _reset: function() {
    this.model  = this.options.model || this.superset.model;
    this.models = this._models();
  },

  // get the models which belong to this collection
  _models: function() {
    // using internal filter method to filter the models that belong to this subset
    return _.filter(_.filter(this.transform(this.superset.models), function(cm) {
      return cm != null;
    }), this.filter);
  }

});


var subsetMethods = ["forEach", "each", "map", "reduce", "reduceRight", "find", "detect", "filter", "select", "reject", "every", "all", "some", "any", "include", "invoke", "max", "min", "sortBy", "sortedIndex", "toArray", "size", "first", "rest", "last", "without", "indexOf", "lastIndexOf", "isEmpty"];

// add common function to this subset
  
_.each(subsetMethods, function(cMethod) {
  Backbone.Subset.prototype[cMethod] = function() {
    return _[cMethod].apply(_, [this._models()].concat(_.toArray(arguments)))
  };
});

example.js

    // holds ALL upload models
    this.collection     = new ncs.collection.UploadCollection();
    
    
    // subset of archived models
    this.archiveCollection  = new Backbone.Subset({
                  superset: this.collection,
                  filter: function(upload) {
                    return (upload.hasFailed() || upload.isComplete());
                  }
                });
            
    // subset of active models
    this.activeCollection = new Backbone.Subset({
                  superset: this.collection,
                  filter: function(upload) {
                    return (upload.isQueued() || upload.isUploading());
                  }             
    });
    
    // subset of queued models
    this.queuedCollection = new Backbone.Subset({
                  debug: 'queued',
                  superset: this.collection,
                  filter: function(upload) {
                    return upload.isQueued();
                  }             
    });

    // subset of active models
    this.uploadingCollection  = new Backbone.Subset({
                    debug: 'uploading',
                    superset: this.collection,
                    filter: function(upload) {
                      return upload.isUploading();
                  }             
    });