Querying for entities with missing properties in app engine Datastore?

问题

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.

回答1:

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.

来源：https://stackoverflow.com/questions/3332080/querying-for-entities-with-missing-properties-in-app-engine-datastore