Dynamically create instance of current collection

Question

Firstly, apologies for the title - if anyone has a better version after reading the question, please edit or ask me to.

I have extended the core Backbone Collection object with a 'where' method that allows me to perform an _.select on the models within the collection. Currently this returns a new vanilla Collection object containing the models. What I want is for the method to return a Collection object of the same type as I am calling ...

Backbone.Collection.prototype.where = function(a) {
  var execute = function(item) {
    ...
  };

  return new Backbone.Collection(this.select(execute));
};

var Accounts = Backbone.Collection.extend({...})

What I want, at the return statement is to be returning a new Account collection. But I don't want to have to define or extend this method in each collection I extend. Something like the following pseudo code:

return new instanceof this(this.select(execute));

Make sense?

Jake Dempsey Jake Dempsey · Accepted Answer · 2011-05-20T03:35:25

Im not 100% sure of what you are asking, but I think you want to run a 'where' on an instance of a collection and get back a NEW collection. Was just playing around in firebug and came up with this:

var Chapter  = Backbone.Model;
var chapters = new Backbone.Collection;

chapters.comparator = function(chapter) {
  return chapter.get("page");
};

chapters.add(new Chapter({page: 9, title: "The End"}));
chapters.add(new Chapter({page: 5, title: "The Middle"}));
chapters.add(new Chapter({page: 1, title: "The Beginning"}));

Backbone.Collection.prototype.where = function(selector) {
 var newCol = new this.__proto__.constructor();
 var itemsToInsert = this.select(selector);
 itemsToInsert.forEach(function(item){ newCol.add(item) });
 return newCol;
};

chapters.where(function(c){ return c.get('page') == 1 });

`

This could probably be done better.. but this seems functional.

Dynamically create instance of current collection

1 Answers