See Array Changes in Firestore Security

问题

I have a collection reviews where each review contains a list of uids of users who have liked it called likes. The schema looks like:

• review (collection)
  • title string
  • author uid
  • likes [uid]
  • posted timestamp
• user (collection) - uid
  • created timestamp
  • email string

Currently, I'm handling a user liking a review with:

    firebase.firestore().doc(rid).update({
      likes: firebase.firestore.FieldValue.arrayUnion(this.fetchCurrentUID())
    });

And unliking with:

    firebase.firestore().doc(rid).update({
      likes: firebase.firestore.FieldValue.arrayRemove(this.fetchCurrentUID())
    });

I only want to let a user add or remove their own uid from likes.

How can I write a security rule to ensure this? Specifically, I need to see how the list is being updated, for instance something like:

let newVals = request.resource.data.new_values // or something
return (newVals.length == 1 && newVals[0] == request.auth.uid)

来源：https://stackoverflow.com/questions/61528403/see-array-changes-in-firestore-security