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    <p>I'm assuming you're receiving a Category/Items list in JSON that looks something like this...</p> <pre><code>{ 'id': 1, 'name': 'My 1st Category', 'children': [ { 'id': 2, 'name': 'My 2nd Category', 'children': [] }, { 'id': 1, 'name': 'An Item', 'price': 109.99 } ] } </code></pre> <p>Backbone.js doesn't have anything out of the box that supports multiple models in a collection, but it also doesn't have any restrictions on the types of models you put in a collection.</p> <p>Specifying the model type in the collection definition only does one thing, it lets Backbone know what model type to create if you pass raw JSON to the collection instead of a <code>Backbone.Model</code> object. If you add an <code>Item</code> model to a collection that already contains a few <code>Category</code> Models, Backbone will have no problem popping it into the models list; it doesn't do any type checking.</p> <p>So with that in mind, you can use just about everything the collection offers except pass it raw JSON; you'll need to handle that yourself. So your choices are to either build up your models beforehand, making them into <code>Backbone.Model</code> objects, or create something that'll do the parsing for you.</p> <p>For the second option, the parser, I'd suggest passing a special variable to the collection that contains your raw JSON, then handling that in your <code>initialize</code> function. Here's an example:</p> <pre><code>var CategoryCollection = Backbone.Collection.extend({ initialize: function(m, models) { _.each(models, function(model) { var modelObject = null; if (model.price !== undefined) { modelObject = new Item(model); } else { modelObject = new Category(model); } this.add(modelObject); }, this); } }); </code></pre> <p>So it is a little hacky, but you determine the type of model based on if it has a specific field (<code>price</code> in my example), create the model object, then add that to the collection.</p> <p>You'd then call it this way:</p> <pre><code>var myCollection = new CategoryCollection([], myJSON); </code></pre> <p>Notice you have to pass an empty array as the first argument since that's how'd you normally pass a set of models to the collection.</p> <p>Later on when using the collection, you can determine if you're dealing with an <code>Item</code> or <code>Category</code> using a simple <code>instanceof</code> check:</p> <pre><code>_.each(myCollection.models, function(model) { if (model instanceof Item) { console.log("It's an Item! Price: ", model.get("price")); } else { console.log("It's a Category!"); } }); </code></pre>
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    1. POImplementing a composite pattern using MVC/Backbone.js
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    1. COneat idea to use the options parameter to smuggle in the raw data.
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    2. COHaha thanks. I thought that'd be easier than hacking the Backbone.js source itself. I guess to clean it up you could always create a wrapper class that you only pass your JSON to which in turn creates and returns the collection for you.
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    3. COYeah, I'd like to hijack/wrap a few other collection methods too, mainly as internally Backbone.Model expects ids to be unique e.g I'd need to adapt id so it either accepts a key value pair {modelType: id}, or the same reduced to a formatted string.
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