code: function(key) {
        var self = this;
        delete this.attributes[key];
        if (this._serverData[key]) {
          this.attributes[key] = this._serverData[key];
        }
        Parse._arrayEach(this._opSetQueue, function(opSet) {
          var op = opSet[key];
          if (op) {
            self.attributes[key] = op._estimate(self.attributes[key], self, key);
            if (self.attributes[key] === Parse.Op._UNSET) {
              delete self.attributes[key];
            } else {
              self._resetCacheForKey(key);
            }
          }
        });
      }
docs: Populates attributes[key] by starting with the last known data from the
  server, and applying all of the local changes that have been made to that
  key since then.