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我有点难以理解我编写的与 Google App Engine 的 NDB 数据存储区的异步 API 一起使用的一些小任务的情况。概述是：我需要汇总用户的购买历史记录，并且“UserPurchase”对象引用购买的“产品”或“自定义”项目，以及购买它的“Establishment”，两者都使用 KeyProperty UserPurchase ndb.Model 中的属性。我想尽可能地并行化各种 NDB 查找，所以我非常接近 NDB 文档（位于https://cloud.google.com/appengine/docs/standard/python/ndb/async）并构建3 个小任务：

@ndb.tasklet
def get_establishment(purch):
    resto = yield purch.p_establishment.get_async()
    ret = {
        "rkey": resto.key.urlsafe(),
        "rname": resto.resto_name
    }
    raise ndb.Return(ret)

@ndb.tasklet
def get_item(purch):
    item = yield purch.p_item.get_async()
    if (purch.p_item.kind() == "Product"):
        ret = {
            "ikey": item.key.urlsafe(),
            "iname": item.name
        }
    else:
        ret = {
            "ikey": item.key.urlsafe(),
            "iname": item.cust_name
        }
    raise ndb.Return(ret)

@ndb.tasklet
def load_history(purch):
    at, item = yield get_establishment(purch), get_item(purch)
    ret = {
        "date": purch.p_datetime,
        "at_key": at.rkey,
        "at": at.rname,
        "item_key": item.ikey,
        "item": item.iname,
        "qty": purch.p_quantity,
        "type": purch.p_type
    }
    raise ndb.Return(ret)

然后，我这样打电话：

pq = UserPurchase.query().order(-UserPurchase.p_datetime)
phistory = pq.map(load_history, limit = 20)

检索最近的 20 次购买以进行显示。但是，当我运行它时，我遇到了一个奇怪的异常，我不知道该怎么做……而且我对 tasklet 以及它们如何工作还不够熟悉，无法自信地说我知道发生了什么。如果有人能给我一些关于寻找什么的指示，我将非常感激......！这是我在运行上述代码时遇到的异常：

      ...
       File "/Programming/VirtualCellar/server/virtsom.py", line 2348, in get
        phistory = pq.map(load_history, limit = 20)
      File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/ndb/utils.py", line 160, in positional_wrapper
        return wrapped(*args, **kwds)
      File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/ndb/query.py", line 1190, in map
        **q_options).get_result()
      File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/ndb/tasklets.py", line 383, in get_result
        self.check_success()
      File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/ndb/tasklets.py", line 624, in _finish
        result = [r.get_result() for r in self._results]
      File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/ndb/tasklets.py", line 383, in get_result
        self.check_success()
      File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/ndb/tasklets.py", line 430, in _help_tasklet_along
        value = gen.send(val)
      File "/Programming/VirtualCellar/server/virtsom.py", line 2274, in load_history
        "at_key": at.rkey,
    AttributeError: 'dict' object has no attribute 'rkey'

基于错误，似乎小任务不喜欢返回字典......

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1 回答 1

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您误解了错误消息：返回了一个 dict，但您试图访问该 dict 不存在的属性。

看来您要访问该字典中的值，而不是该字典的属性，如果是这样，则在内部进行更改load_history：

        "at_key": at.rkey,

至：

        "at_key": at.get('rkey'),

或者：

        "at_key": at['rkey'],

您还想重新访问其他类似的尝试来访问at和itemdicts 中的其他 dict 值。

于 2017-03-25T16:11:40.697 回答