问题
I would like to use data in the realtime database to allow user access in the firestore database. Is it possible to reference nodes in the realtime database from the firestore security rules?
回答1:
It is currently not possible to cross between database products like this in security rules. Please feel free to file a feature request for this.
You can, however, write code to run on Cloud Functions that deals with database changes after the change has happened, and undo or restrict the change there.
来源：https://stackoverflow.com/questions/58043947/referencing-firebase-realtime-database-data-through-firestore-security-rules