当实体明确存在于数据存储中时，GAE 返回 Nonetype

Question

当用户创建一个新事件时，他们输入“event_name”和“event_time”并从下拉列表中选择位置。然后，我从与该位置匹配的 PlaceModel 实例中检索事件的纬度和经度。

问题是，当我要查找的 PlaceModel 实例存在时，localhost 返回 Nonetype。

我的模型：

class PlaceModel(db.Model):
    place_name = db.StringProperty(required = True)
    place_lat = db.StringProperty(required = True)
    place_long = db.StringProperty(required = True)
    def render(self):
        return render_str("placemodel.html", p = self)

class EventModel(db.Model):
    event_place = db.ReferenceProperty(PlaceModel)

    event_name = db.StringProperty(required = True)
    event_time = db.StringProperty(required = True)
    def render(self):
        return render_str("eventmodel.html", e = self)

html:

<select name = "place_name">
{% for place in allplaces %}
    <option name = "place_name" value = {{place_name}}> {{place.place_name}}</option>
{%endfor%}
</select>

蟒蛇：

class NewEvent(Handler):
   def get(self):
        if self.user:
            allplaces = PlaceModel.all()
            self.render("newevent.html", allplaces = allplaces)
        else:
            self.redirect("/signup")

   def post(self):
        event_name = self.request.get("event_name")
        event_time = self.request.get("event_time")
        place_name = self.request.get_all("place_name")

        if event_name and event_time and place_name:
            place_lat = PlaceModel.gql("where place_name = :place_name", place_name = place_name).get().place_lat
            place_long = PlaceModel.gql("where place_name = :place_name", place_name = place_name).get().place_long

            event_place = PlaceModel(parent = place_key(), 
                            place_name = place_name, place_lat = place_lat, place_long = place_long)

            event = EventModel(parent = event_key(),
                    event_name = event_name, event_time = event_time, 
                    event_place = event_place)

            event.put()
            stat = "your event has been recorded"
            self.render('newevent.html', stat = stat)
        else:
            allplaces = PlaceModel.all()

            error = "fill in all the boxes"
            self.render("newevent.html", error = error, allplaces = allplaces,
                        event_name = event_name, event_time = event_time)

怎么了？？为什么 gql 返回 nonetype？

编辑： 错误日志的（后半部分）：

File "/Users/yingjiefu/Documents/munchkin/munchkin.py", line 195, in post
    place_lat = PlaceModel.gql("where place_name = :place_name", place_name = place_name).get().place_lat
AttributeError: 'NoneType' object has no attribute 'place_lat'

编辑：现在可以使用了！

蟒蛇：

class NewEvent(Handler):
   def get(self):
        if self.user:
            allplaces = PlaceModel.all()
            self.render("newevent.html", allplaces = allplaces)
        else:
            self.redirect("/signup")

   def post(self):
        event_name = self.request.get("event_name")
        event_time = self.request.get("event_time")
        place_name = self.request.get("place_name")

        if event_name and event_time and place_name:
            place = PlaceModel.all().filter("place_name", place_name).get()
            place_lat = place.place_lat
            place_long = place.place_long


            event = EventModel(parent = event_key(),
                    event_name = event_name, event_time = event_time, 
                    event_place = place)

            event.put()
            stat = "your event has been recorded"
            allplaces = PlaceModel.all()
            self.render('newevent.html', stat = stat, allplaces = allplaces)
        else:
            allplaces = PlaceModel.all()

            error = "fill in all the boxes"
            self.render("newevent.html", error = error, allplaces = allplaces,
                        event_name = event_name, event_time = event_time)

html:

<select name = "place_name" >
{% for place in allplaces %}
    <option value = "{{ place.place_name }}">{{ place.place_name }}</option>
{% endfor %}
</select>

Answer 1

这段代码有很多问题。

我希望主要在于您如何定义选项中的值。您不仅没有用引号括起来，而且实际上使用了一个不存在的变量：place_name。它应该是这样的：

<option name="place_name" value="{{place_name}}">{{place.place_name}}</option>

其次，在从请求中提取 place_name 值时使用 get_all()。据我了解，它返回一个 list，因此您将在 GQL 的占位符中有多个值。您应该使用get()，就像对其他变量一样。

第三，与您的问题无关，但您为什么要两次执行完全相同的查询？无缘无故地花费你两倍的成本。获取一次并将其存储在变量中：

place = PlaceModel.gql("where place_name = :place_name", place_name=place_name).get()
place_lat = place.place_lat
place_long = place.place_long

（我什至不会问您为什么要使用 GQL 而不是普通的 Query 语法，后者会更短：PlaceModel.all().filter('place_name', place_name) - 您确实意识到它们都被翻译成相同的 RPC 调用，而 GQL 不是'不比模型版本更“原生”吗？）