Per field rules in Firestore Security Rules

问题

I have a bunch of documents that contain a few fields each. How can I write rules that only apply to a specific field in each document?

For example, if my documents looked like this:

{
  "displayName": "John Doe", // read and write
  "accessLevel": 3 // read only
}

How could I make it so that you can

• Read display name and access level
• Write to the display name
• Not write to the access level

I've gone through a lot of videos and Firestore docs and haven't found anything that shows how you would exercise this per-field control.

回答1:

What you're looking for is to make a field non-modifiable. You do that by checking in your rules that the value of the field is the same after the request as before it.

I have a simple helper function for this in my rules:

function isUnmodified(key) {
  return request.resource.data[key] == resource.data[key]
}

I then call this function from within my write (or create and update) rules:

  allow update: if isAdmin() || isUnmodified('name');

So in my example above, any admin (as determined by my isAdmin function) can modify the name field, but other users can't.

来源：https://stackoverflow.com/questions/58423627/per-field-rules-in-firestore-security-rules