code: function(key) {
        var value = this.attributes[key];
        if (_.isObject(value) &&
            !(value instanceof Parse.Object) &&
            !(value instanceof Parse.File)) {
          value = value.toJSON ? value.toJSON() : value;
          var json = JSON.stringify(value);
          if (this._hashedJSON[key] !== json) {
            this._hashedJSON[key] = json;
            return true;
          }
        }
        return false;
      }
docs: Replaces the cached value for key with the current value.
  Returns true if the new value is different than the old value.