javascript - 尝试创建自定义类型并添加实例时出错

Question

 function initializeModel(model) {

   Book = function() {}
   Book.prototype.title = gapi.drive.realtime.custom.collaborativeField('title');
   Book.prototype.author = gapi.drive.realtime.custom.collaborativeField('author');
   Book.prototype.isbn = gapi.drive.realtime.custom.collaborativeField('isbn');
   Book.prototype.isCheckedOut = gapi.drive.realtime.custom.collaborativeField('isCheckedOut');
   Book.prototype.reviews = gapi.drive.realtime.custom.collaborativeField('reviews');
   gapi.drive.realtime.custom.registerType(this.Book, 'Book'); 


   //Error begin  from  here
   var book = model.create('Book');
   book .title = "hello,waiter"
   model.getRoot().set('book', book);

 }

在 chrome 控制台中它提醒我：

Drive Realtime API 错误：invalid_compound_operation：在同步块结束时打开复合操作 - 您是否忘记调用 endCompoundOperation()？

我在哪里犯错？谁能给我一个通过google drive realtime api创建自定义类型的例子？