Sync

Backbone.sync is the function that Backbone calls every time it attempts to read or save a model to the server. By default, it uses jQuery.ajax to make a RESTful JSON request and returns a jqXHR. You can override it in order to use a different persistence strategy, such as WebSockets, XML transport, or Local Storage.

The method signature of Backbone.sync is sync(method, model, [options])

method – the CRUD method ("create", "read", "update", or "delete")
model – the model to be saved (or collection to be read)
options – success and error callbacks, and all other jQuery request options

With the default implementation, when Backbone.sync sends up a request to save a model, its attributes will be passed, serialized as JSON, and sent in the HTTP body with content-type application/json. When returning a JSON response, send down the attributes of the model that have been changed by the server, and need to be updated on the client. When responding to a "read" request from a collection (Collection#fetch), send down an array of model attribute objects.

Whenever a model or collection begins a sync with the server, a "request" event is emitted. If the request completes successfully you'll get a "sync" event, and an "error" event if not.

The sync function may be overridden globally as Backbone.sync, or at a finer-grained level, by adding a sync function to a Backbone collection or to an individual model.

The default sync handler maps CRUD to REST like so:

create → POST /collection
read → GET /collection[/id]
update → PUT /collection/id
patch → PATCH /collection/id
delete → DELETE /collection/id

As an example, a Rails 4 handler responding to an "update" call from Backbone might look like this:

def update
  account = Account.find params[:id]
  permitted = params.require(:account).permit(:name, :otherparam)
  account.update_attributes permitted
  render :json => account
end

One more tip for integrating Rails versions prior to 3.1 is to disable the default namespacing for to_json calls on models by setting ActiveRecord::Base.include_root_in_json = false

ajaxBackbone.ajax = function(request) { ... };
If you want to use a custom AJAX function, or your endpoint doesn't support the jQuery.ajax API and you need to tweak things, you can do so by setting Backbone.ajax.

emulateHTTPBackbone.emulateHTTP = true
If you want to work with a legacy web server that doesn't support Backbone's default REST/HTTP approach, you may choose to turn on Backbone.emulateHTTP. Setting this option will fake PUT, PATCH and DELETE requests with a HTTP POST, setting the X-HTTP-Method-Override header with the true method. If emulateJSON is also on, the true method will be passed as an additional _method parameter.

Backbone.emulateHTTP = true;

model.save();  // POST to "/collection/id", with "_method=PUT" + header.

emulateJSONBackbone.emulateJSON = true
If you're working with a legacy web server that can't handle requests encoded as application/json, setting Backbone.emulateJSON = true; will cause the JSON to be serialized under a model parameter, and the request to be made with a application/x-www-form-urlencoded MIME type, as if from an HTML form.

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