Make backbone model fetch discard missing fields

Question

Let's say I have a Backbone model that when fetch() is called (for that specific model, not the entire collection) it gets this from the server:

{ a: "val-1", b: "val-2" }

Later, I call fetch() on the model again, and this time the server returns:

{ b: "val-x", c: "val-y" }

At this point, I would like my model to have this state, because that's the latest state provided by the server:

{ b: "val-x", c: "val-y" }

However, my Backbone model has this state instead:

{ a: "val-1", b: "val-x", c: "val-y" }

How do I fetch() a model in Backbone so that the resulting state is exactly what is returned from the server, and doesn't include old obsolete fields?

Atlas Atlas · Accepted Answer · 2013-05-06T22:18:19

I discovered that one way to get the desired behavior is by adding this parse function to the model in question:

parse: function(resp) {
  for (var key in this.attributes) {
    if (resp[key] === undefined) {
      resp[key] = undefined;
    }
  }

  return resp;
}

If the response from the server lacks an attribute that's in the local model, it explicitly adds that key to the response with an undefined value. This causes fetch() to behave correctly and remove it from the model.

Make backbone model fetch discard missing fields

2 Answers