python - 谷歌应用引擎: empty property in datastore

Question

假设我有一个模型:

class A(db.Model):
    B = db.StringProperty()
    C = db.StringProperty()

如果我想使用 python 搜索 C 中的所有空属性(不是无，只是空)，如何查询？

Answer 1

来自GAE Python documents

It is not possible to perform a query for entities that are missing a given property. One alternative is to create a fixed (modeled) property with a default value of None, then create a filter for entities with None as the property value.