Firestore security rules: How to validate that a field is undefined?

Question

When a user signs up and they initialise their data in firestore, I want to validate that they aren\'t attempting to set their role (i.e. so they\'re not setting it to \'adm

Answer 1

Use the in operator to find out if a property of an object doesn't exist.

!("role" in request.resource.data)

This yields a boolean. See it in the rules API docs for the Map type.