sebelga
Support 'IN' operator
It would be great to support IN operator, where the right hand side is a list of values. Since the Datastore client doesn't natively support that, this library would need to split into multiple queries, and then merge the results. In fact, the original App Engine Datastore clients do just that:
https://cloud.google.com/appengine/docs/standard/java/datastore/queries#filters
https://cloud.google.com/appengine/docs/standard/python/datastore/queryclass#Instance_Methods
As an aside, the Python ndb library also supports IN operator:
https://googleapis.dev/python/python-ndb/latest/query.html#
In code it calls it a DisjunctionNode:
https://github.com/googleapis/python-ndb/blob/master/google/cloud/ndb/query.py#L637-L650
This operator should work either on a scalar value field, or on a list value field.
