Discussion on: Restrict specific fields updation in Firebase Firestore

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Thanks for this @ Kushagra, really helpful!

I had a situation where I had to secure the fields of a Firestore map. This is what I got so far, which so far is testing well with various scenarios of map/field combinations. The final piece of the puzzle was ensuring an empty object could not be passed to the Firestore map as it would overwrite all the "good work" of the rules.

function notUpdatingNested(fsmap, field) {
      return 
      !(request.resource.data[fsmap] == {})
      && (((!(fsmap in resource.data) || !(fsmap in request.resource.data) )
        || (!(field in resource.data[fsmap]) || !(field in request.resource.data[fsmap])))
      || (resource.data[fsmap][field] == request.resource.data[fsmap][field]))
    }

This is my initial effort (being fairly new to Firestore) so would appreciate feedback/corrections, or better ways ;)

Tomas Rimkus • Nov 13 '20

You could simplify this by using "MapDiff":

function notUpdatingNested(fsmap, field) {
    return !(fsmap in request.resource.data) 
        || (
            (request.resource.data[fsmap] is map)
            && (fsmap in resource.data)
            && !(request.resource.data[fsmap].diff(resource.data[fsmap]).affectedKeys().hasAny([field]))
        )
}