谷歌应用程序引擎ndb：放（）然后查询（），总是有一个较少的项目 [英] google app engine ndb: put() and then query(), there is always one less item

问题描述

我想知道是否有人在Google App Engine NDB上遇到了一个奇怪的问题：在创建一个新实体并通过 put（）保存它之后，然后立即执行 query（），总会有一个更少的项目。例如，

I wonder if anybody has encountered the strange problem on Google App Engine's NDB: after creating a new entity and saving it by put(); and then query() immediately, there is always one less item. For example,

class Item(ndb.Model):
    ...
    ...

items = Item.query().fetch()
length1 = len(items)
item = Item()
item.put()
items = Item.query().fetch()
length2 = len(items)

在上面， length1 总是等于 length2 。但是，稍后重新访问相同的HTML页面时， length2 将被更正。问题是什么？感谢。

In the above, length1 is always equal to length2. However, length2 will be corrected when revisiting the same HTML page later. What is the problem? Thanks.

推荐答案

我通过进行适当的查询，创建新模型记录，然后在返回之前将其追加到我的查询它。修改你的，看起来像：

I solved this by making the appropriate query, creating the new model record, then appending it to my query before returning it. Modifying yours, it looks like:

class Item(ndb.Model):
    ...
    ...

items = Item.query().fetch()
length1 = len(items)
item = Item()
item.put()

appended_items = list()
for existing_item in items:
    appended_items.append(existing_item)

appended_items.append(item)
length2 = len(appendeditems)

在这种情况下，attached_items包含您的查询，加上新元素。列表生成效率低下，但是我是一个python / ndb noob，可能有一种方法可以将Query Collection中的Collection取出来，这样会更好。

In this case, appended_items has your query, plus the new element. The list generation is inefficient, but I'm a python/ndb noob and there's probably a way to get the Collection right out of the Query model, which would be much better.

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