Merge local Backbone collection with server

Question

I have a local Backbone collection:

var collection = new Backbone.Collection([ { greeting: "hi" }, { greeting: "bye" } ]);

I understand that when I run collection.fetch, Backbone will run collection.set on the results. I need to merge in the response from the server, however. Say the response is:

[ { id: "2", greeting: "hi", name: "Bob" } ]

I would like the resulting collection, after the merge, to be:

[ { id: "2", greeting: "hi", name: "Bob" }, { greeting: "bye" } ]

I understand Backbone already attempts to do some merging here, but if I set the example response above, no merge happens and a new model gets added instead. I assume this is because it merges by id, and here we do not have any ids (in the local collection). In this case, greeting is my unique identifier / key.

The reason I am trying to do this is because I have a local collection and I simply want to see what already exists from that collection (using the key greeting) and merge any findings in.

Answer 1

My solution:

feeds.fetch({
  add: false,
  remove: false,
  merge: false,
  data: params,
  success: function (feeds, response) {
    // Merge any matches
    _.each(response.results, function (result) {
      _.each(feeds.models, function (feed) {
        // We have to `parse` the result before setting it, as Model#set does
        // not automatically run `parse` (Collection#set does).
        result = feed.parse(result)
        if (feed.get('rssUrl') === result.rssUrl) feed.set(result)
      })
    })
    cb(feeds)
  }
})