Backbonejs updating Model with idAttribute set to Id - asp.net-mvc

Question

I'm trying to update a backbone model, the server side is asp.net mvc 4. I'm getting:
"System.ArgumentException: An item with the same key has already been added" exception.
The reason is because backbone is sending Id and id to the server as properties, and the JsonValueProvider tries to add this to a dictionary.
Here is my model:
var Task = Backbone.Model.extend({
url: "/tasks/task",
idAttribute: "Id"
});
This is send to the server via Put request:
{"Id":294912,"Task":"test","DueDate":"2012-03-24T02:00:00.000Z", "id":294912}
Is there a way to prevent backbone in sending the "id" property?

Answer 1

The problem here is because the conventions in C# is not the same as in JavaScript. In C# classes have properties that starts with capital letters (Pascal Case) and it's the norm in JavaScript to start your properties in lower case (Camel Case).
Thus when serializing view models the default behavior of the JSON.NET serializer is to serialize the object exactly with the same capitalization of properties. I could rename the properties on the view model to be camel case, but it would be as "weird" as to have properties with pascal case in your JavaScript objects.
So instead to force Backbone into a non convention way, I've change the serialization of the objects to convert the Pascal case properties into Camel case properties by leveraging JSON.NET's Contract Resolver functionality.
var settings = new JsonSerializerSettings();
settings.ContractResolver = new CamelCasePropertyNamesContractResolver();
JsonSerializer serializer = JsonSerializer.Create(settings);
JsonConvert.SerializeObject(object, Formatting.None, settings);
Now this creates consistency on the client side with my code and with all the cool libraries out there.

Answer 2

Sounds to me like the issue is in your server-side code, not with the call from Backbone. A PUT is an edit operation on the server, so you're updating an existing entity. You need the ID property to identify the model on the server and update the properties that have changed.
If ASP.NET MVC is complaining that the model already exists in the database, you are trying to do an INSERT instead of an UPDATE. We'd need to see the controller and data access code to see where things are going awry.
UPDATE: What happens if you leave off the idAttribute property? From the Backbone documentation:
A special property of models, the id is an arbitrary string (integer id or UUID).
If you set the id in the attributes hash, it will be copied onto the model as a
direct property.
The id attribute should be sent by default; it looks like you're forcing it to be included a second time.
Under idAttribute in the docs:
A model's unique identifier is stored under the id attribute. If you're directly communicating
with a backend (CouchDB, MongoDB) that uses a different unique key, you may set a Model's
idAttribute to transparently map from that key to id.
ASP.NET MVC's model binding should be able to cope with id vs. Id.
UPDATE: Found a good blog post that describes using a view model to aid in serializing your C# objects into the format Backbone expects. This seems like a reasonable, if slightly annoying, solution.