如何干净地删除 ndb 属性 [英] how to cleanly remove ndb properties

问题描述

在我的应用程序中，我需要删除一些模型属性.
我查看了 此链接，但第一个问题是这些属性位于 上polymodel 并且我无法切换到 expando 来删除属性，我什至不知道如果我更改 polymodel 到 expando.

in my app i need to remove a few of my models properties.
i checked out this link but the first issue is that the properties are on a polymodel and there is no way im going to switch to an expando for the time to remove the properties, im not even shure what could happen if i change a polymodel to an expando.

那么如何从现有实体中删除属性?

so how do i remove properties from existing entities?

我想将所有 StringProperty 设置为 None，然后从模型架构中删除它们并重新部署.其中一个属性是 BooleanProperty，我不能将其设置为 None 对吗?！或 ndb.PickleProperty... 我应该如何删除它?

i was thinking to set all StringProperty to None and then remove these from the model schema and redeploy. one of those properties is a BooleanProperty, i can't set this one to None right?! or an ndb.PickleProperty... how should i remove that?

有人知道如何正确完成这项工作吗?

does anybody know how to get this done properly?

推荐答案

如果您想更新所有实体，推荐的方法是读取和重写所有实体的 map/reduce 作业；但是它可能不值得，这取决于你有多少数据——map/reduce 也不是免费的.

If you want to update all your entities the recommended approach is a map/reduce job that reads and rewrites all entities; however it may not be worth it, depending on how much data you have -- the map/reduce isn't free either.

还要确保在一小部分数据上测试 map/reduce 作业.从实体中真正删除一个属性是非常微妙的，即使它不再在模型类中！最好的方法可能是:

Also be sure you test the map/reduce job on a small subset of the data. It is remarkably subtle to truly remove a property from an entity, even if it's not in the model class any more! The best approach may be:

if 'propname' in ent._properties:
  del ent._properties['propname']
  ent.put()

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