在应用引擎数据存储中查询缺少属性的实体？ [英] Querying for entities with missing properties in app engine Datastore?

问题描述

  class示例（db.Model）：
 row_num = db.InteProProperty（required = True）
 updated = db.IntegerProperty（）
 ... 
 ... 
  

现在，当我存储值时，我可能无法每次填充更新属性的值，这意味着在某些实体中它可能不存在。

我想构建一个数据存储查询，以便我可以获取没有属性更新集的所有类实例。

我该怎么做？

p.s。我知道我可以设置一个默认值，然后查询它。但问题是我有超过300万个实体，并且更新将仅标记为1％，因此我不想通过将其余的设置为0来浪费太多的数据存储空间。

<在GQL中，没有属性值的对象不能通过该属性的查询返回，所以如果没有默认值，你所要求的是不可能的 b
参考资料：此页面。

I have a model which looks like this:

class Example (db.Model) :
 row_num = db.IntegerProperty(required=True)
 updated = db.IntegerProperty()
 ...
 ...

Now when i store values, I may not fill the value for the updated property every time, which implies that in some entities it may not exist.

I want to construct a datastore query so that i can get all entities of kind Example which do not have the property updated set.

How do i do this?

p.s. i know i can set a default value and then query on it. But the issue is i have over 3 million entities and updated will be marked only for 1% of them, so i do not want to waste so much of datastore space by setting the rest to 0.

解决方案

In GQL, objects which do not have a value for a property cannot be returned by queries on that property, so what you're asking for is impossible without a default value.

Reference: section headed "Entities Without a Filtered Property Are Never Returned by a Query" on this page.

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