Backbone.js unique attribute name across all models in collection for permalink
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I would like to make sure that a specific attribute is unique across the collection when a new model is created so that I can ultimately use this attribute as a permalink. 

I have a List Collection and List Model. (CoffeeScript)

    class App.Models.List extends Backbone.Model
      defaults:
        name: "My New List"
    
    class App.Collections.ListSet extends Backbone.Model
      model: App.Models.List


When a new model is added to the ListSet, I would like to add a auto-incrementing number to the end of the name attribute if a model exists with that name already. For example `My New List 1` if a model existed with `My New List`. 

I don't want it to be obtrusive and show an error, but just fix the problem automatically. I am happy with the logic behind adding the incrementing integer, but I need direction on where to put the code to make the changes.
