Allow update on single field in firestore

Question

I want to give a user the right to update a document. But ONLY if the user updates one specific field of this document. All other fields shouldn\'t be changed by this user.<

Answer 1

the same answer of "Scott Crossen" with little change, to be more genric

function isUpdateToOpenField(attr) {
    return request.resource.data.diff(resource.data).affectedKeys().hasOnly([attr]);
}

allow update: if isUpdateToOpenField('open');