subModelTypes as class references instead of string class names

[ghost]

Why subModelTypes classes can be only strings?
Is it possible/correct to have subModelTypes class references?

For example this code

Mammal = Animal.extend({
    subModelTypes: {
        'primate': 'Primate',
        'carnivore': 'Carnivore'
    }
});

Primate = Mammal.extend();
Carnivore = Mammal.extend();

MammalCollection = AnimalCollection.extend({
    model: Mammal
});

to work the same as this

Mammal = Animal.extend({
    subModelTypes: {}
});

Primate = Mammal.extend();
Mammal.prototype.subModelTypes.primate = Primate;

Carnivore = Mammal.extend();
Mammal.prototype.subModelTypes.carnivore = Carnivore;

MammalCollection = AnimalCollection.extend({
    model: Mammal
});

---

In our application, we create a base class, send it in event, anyone can listen the event and register its subClass

// file: events.js
(function(){
  window.events = {};
  _.extend(window.events, Backbone.Events);
})();

// file: primate.js
(function(){
  events.on("register:mammals", function(Mammal) {
    var Primate = Mammal.extend({defaults: {title: 'Primate'}});
    Mammal.prototype.subModelTypes.primate = Primate;
  });
})();

// file: carnivore.js
(function(){
  events.on("register:mammals", function(Mammal) {
    var Carnivore = Mammal.extend({defaults: {title: 'Carnivore'}});
    Mammal.prototype.subModelTypes.carnivore = Carnivore;
  });
})();

// file: mammals.js
(function(){
  var Mammal = Backbone.RelationalModel.extend({
    subModelTypes: {}
  });

  events.trigger("register:mammals", Mammal);

  var MammalCollection = Backbone.Collection.extend({
    model: Mammal
  });

  var mammals = new MammalCollection;
  mammals.reset([{type: 'primate'}, {type: 'carnivore'}]);

  console.log(mammals.toJSON());
  console.log(
    mammals.at(0).get('type'),
    mammals.at(0) instanceof Mammal.prototype.subModelTypes[mammals.at(0).get('type')], 
    mammals.at(0).get('title')
  );
  console.log(
    mammals.at(1).get('type'),
    mammals.at(1) instanceof Mammal.prototype.subModelTypes[mammals.at(1).get('type')],
    mammals.at(1).get('title')
  );
})();

---

If I change the getObjectByName method from

getObjectByName: function( name ) {
    var parts = name.split( '.' ),
        type = null;

    ...
}

to

getObjectByName: function( name ) {
    if (name.prototype instanceof Backbone.RelationalModel) {
        return name;
    }

    var parts = name.split( '.' ),
        type = null;

    ...
}

then the example above seems to work. But I am not sure if it's the right way to do this. Also I don't know how this will affect the store.

---

Because it is not possible to have subModelTypes as class references, we did this:

• Instead of registering {'type': ClassReference} in the subModelTypes property, we created a custom property MammalCollection.types = {}; and register there the subTypes.
• Then we made the MammalCollection.model a function that is called on .reset() and search class by type in MammalCollection.types and return the model instance

Then we faced the problem that MammalCollection.model is replaced by Backbone-relational. More details in #472

[ghost]

I created a pull request with some tests in case you will accept this feature. If this is not the way it should be solved, fell free to close that pull request

[hippich]

This looks like a right change.