AppEngine: 模型不是不可变的

Question

我正在尝试把一个模型的实例插入到ndb数据库中。

但是它总是给我一个“模型不是不可变的”的错误提示。

我试过用不同的模型名称，但还是出现同样的错误。

class User(ndb.Model):
    username = ndb.StringProperty()
    email = ndb.StringProperty()
    lwr_username = ndb.ComputedProperty(lambda self: self.username.lower())
    lwr_email = ndb.ComputedProperty(lambda self: self.email.lower())

这是我的插入代码：

entity = User()
entity.email = ""
entity.username = "bob"

logging.info(entity)

#Commit data asynchronously
entities = [entity]
futures = ndb.put_multi_async(entities)

#Build Response whilst database is committing
response = {

}

#Wait for commits to finish
ndb.Future.wait_all(entities)

这是完整的错误追踪信息：

Model is not immutable
Traceback (most recent call last):
  File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1511, in __call__
    rv = self.handle_exception(request, response, e)
  File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1505, in __call__
    rv = self.router.dispatch(request, response)
  File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1253, in default_dispatcher
    return route.handler_adapter(request, response)
  File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1077, in __call__
    return handler.dispatch()
  File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 547, in dispatch
    return self.handle_exception(e, self.app.debug)
  File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 545, in dispatch
    return method(*args, **kwargs)
  File "/base/data/home/apps/s~myapp-api/1.377037445874907069/v1/handler/userHandler.py", line 11, in post
    responseCode, response = UserService.create(locale, json.loads(self.request.body), **kwargs)
  File "/base/data/home/apps/s~myapp-api/1.377037445874907069/v1/service/userService.py", line 37, in create
    ndb.Future.wait_all(entities)
  File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 345, in wait_all
    waiting_on = set(futures)
  File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 3017, in __hash__
    raise TypeError('Model is not immutable')
TypeError: Model is not immutable

Answer 1

你需要使用 futures 列表，而不是 entities，来等待异步处理完成：

ndb.Future.wait_all(futures)

wait_all() 函数会把这些存储在一个 set() 对象里，而集合（set）要求里面的内容是可哈希的。因为可变对象不能存放在集合或字典里，所以谷歌的工程师在 Model.__hash__ 方法中添加了一个明确的 TypeError，这就是你在这里看到的错误。