                     break
             break if found != -1
         found
+
+    sum: ->
+        args = _.toArray(arguments)
+        args.unshift(this.models)
+        return _.sum.apply(_, args)
 
     # convenience method to create a new subCollection
     subcollection: (options) ->

        else
            this.sync('read', this, options)

    # Fetch a single model with the given id
    fetchId: (id, options = {}) ->
        this.sync('read', this, _.extend({
            limit: 1, query: {"#{@model::idAttribute}": id}
        }, options))

            )
            return this
        )

    # replace these models from other collection
    copyFrom: (collection) ->
        this.set(collection)


}

