save_changes.coffee

save_changes_common =

  sync: (method, model, options) ->

    if method == 'update' && model.changedAttributes()
      options.data = JSON.stringify(model.changedAttributes())
      options.contentType = 'application/json';
    Backbone.sync.call(this, method, model, options)

save_changes_model =

  saveChanges: (key, value, options) ->
    self = this
    if _.isObject(key) || key == null
      attrs = key
      options = value
    else
      attrs = {}
      attrs[key] = value
    `options = options ? _.clone(options) : {}`
    _.extend options, { wait: true }
    actually_changed = _.any attrs, (value, key)->
      value != self.get key
    if actually_changed
      @save attrs, options
      @set  attrs

_.extend Backbone.Model.prototype, save_changes_common, save_changes_model
_.extend Backbone.Collection.prototype, save_changes_common