Question 120349 in Firebase Question posted in
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Firebase – Firestore rules – How to allow create but not update?

Here’s what I’ve written;

rules_version = '2';

service cloud.firestore {
  match /databases/{database}/documents {
    match /reservedUsernames/{username} {
      allow update: if false;
      allow create: if request.auth != null;
    }
  }
}

I already added a document with ID sam and a field userId = 122. If I run an update on that document, see how below, it succeeds! How can I allow creations but no updates?

db.collection("reservedUsernames")
  .document(searchableUsername)
  .setData(["userId": userId])
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2

Answers


  1. Chosen as BEST ANSWER
    0

    I managed to do it by using Security Rules:

    rules_version = '2'

service cloud.firestore {
  match /databases/{database}/documents {
    match /reservedUsernames/{documentId} {
      allow create: if request.auth != null && existingData(resource) == null
    }

    function incomingData(request) {
      return request == null || request.resource == null || request.resource.data == null ? null : request.resource.data
    }

    function existingData(resource) {
      return resource == null ? null : resource.data
    }
  }
}

    This way I check if I'm updating an existing document and it passes only if I'm not!


  2. 0

    When using:

    .setData(["userId": userId])

    It means that you’re setting the data, and not updating it. The following rule:

    allow update: if false;

    Indeed rejects all update operations but as @DougStevenson mentioned in his comment, having it in your rules it’s the exact same thing as not having it at all, because by default the rules are set to false.

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