Enforcing unique userIds in Firebase Firestore

问题

I'm playing around with the new Firestore database from Firebase and was wondering if there was a more efficient way to enforce unique usernames (or unique child nodes).

I use email/password auth but allow users to create a unique handle, like Twitter.

With the Realtime database I was able to achieve this with transactions and a multiple node structure.

-users
    -uid1234:
        -username: ryan

-usernames:
    -ryan: uid1234

I was thinking it may be possible to do this without the extra usernames node using documents as the username in Firestore.

回答1:

You could do it probably do it in 2 ways. Check with a separate call before create user, if the user exist in an collection with usernames.

Also you could create a rule like:

match /users/{document=**} {
    allow create: if !exists(/databases/$(database)/documents/usernames/$(request.resource.data.username));
}

In that case you get a error back if the username already exist on creating and that you can catch in the code.

来源：https://stackoverflow.com/questions/47298750/enforcing-unique-userids-in-firebase-firestore