问题描述
我希望能够运行如下查询:MyModel.query(MyModel.some_property == None)并获得结果.我知道如果不将default=<some default>放在属性中，将无法查询它，但是如果设置了default=None，它将为它编制索引吗?
I'd like to be able to run a query like: MyModel.query(MyModel.some_property == None) and get results. I know that if I don't put a default=<some default> in a property, I won't be able to query for it, but if I set default=None will it index it?
类似地，将值设置为None是否会使属性在ndb.Model中建立索引?如果将some_keyword_arg=None传递给构造函数怎么办?
Similarly, does setting values to None cause properties to be indexed in ndb.Model? What if you pass some_keyword_arg=None to the constructor?
我知道做类似ndb.StringProperty(default='')的事情意味着您可以查询它，只是不清楚使用None的语义.
I know that doing something like: ndb.StringProperty(default='') means you can query on it, just not clear on the semantics of using None.
推荐答案
将属性显式设置为None定义一个值，是的，默认情况下有效，该属性将被索引.假设None是特定属性类型的有效值.
Explicitly setting a property to None is defining a value, and yes defaults work and the property will be indexed. This assumes None is a valid value for a particular property type.
正如您指出的那样，会出现一些问题，通常您将None用作标准值，那么如何区分未提供的值和显式的None?
Some issues will arise, as you pointed out, often you use None as a sentinal value, so how do you tell between no Value provided and an explicit None?
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