NDB: Query for unset properties?
app-engine-ndb, google-app-engine, google-cloud-datastore, python
Solution
The Datastore distinguishes between an entity that does not possess a property and one that possesses the property with a null value (None).
It is not possible to query for entities that are specifically lacking a given property. One alternative is to define a fixed (modeled) property with a default value of None, then filter for entities with None as the value of that property.
Problem
I've had some data being gathered in production for a couple of days with, lets say, the following model: ``` class Tags(ndb.Model): dt_added = ndb.DateTimeProperty(auto_now_add=True) s_name = ndb.StringProperty(required=True, indexed=True) ``` Imagine I now add a new property to the model: ``` class Foo(ndb.Model): is_valid = ndb.BooleanProperty(default=False) some_key = ndb.KeyProperty(repeated=True) class Tags(ndb.Model): dt_added = ndb.DateTimeProperty(auto_now_add=True) name = ndb.StringProperty(required=True, indexed=True) new_prop = ndb.StructuredProperty(Foo) ``` ... and gather some more data with this new model. So now I have a portion of data that has the property `new_prop` set, and another portion that does not have it set. My question is: how to I query for the data with the new property `new_prop` NOT set? I've tried: ``` query_tags = Tags.query(Tags.new_prop == None).fetch() ``` But does not seem to get the data without that property set... Any suggestions? Thanks!