Array for ember data that allows extending with findQuery results

expandable_record_array.coffee

DS.ExpandableRecordArray = DS.RecordArray.extend
  isLoading: false

  load: (array) ->
    @set 'isLoading', true
    self = this

    observer = ->
      if @get 'isLoaded'
        content = self.get 'content'

        array.removeObserver 'isLoaded', observer
        array.forEach (record) ->
          clientId = record.get 'clientId'
          unless content.contains clientId
            content.pushObject clientId

        @set 'isLoading', false

    array.addObserver 'isLoaded', observer

usage.coffee

array = DS.ExpandableRecordArray.create
  type: App.Todo
  content: Ember.A([])
  store: App.store

array.load App.store.find(App.Todo, {})
array.load App.store.find(App.Todo, {some_param: true})