Restrictions When Using Google Datastore
When using NoSQL selection rules at a Google Datastore NoSQL database, the following restrictions apply:
Use of OR is not supported.
Use of the ≠, Exists, and Does not exist operators is not supported.
If more than one column is referenced in a rule’s criteria, a Datastore composite index covering the columns in question must be configured prior to rule execution.
If any of the above are not observed, rule execution will fail.