Add default username to User on signup?

[dasveloper]

I'm using Next Auth with Prisma, and Email, Google, and Facebook providers. I'd like all users to have default unique username, something like 'User-1', 'User-2', etc. or 'User-ABCD', and allow users to update their username later. I'm wondering where is the best place to add this logic?

I've added the property to my User model:
username String @unique

But I can't figure out where I should catch the signup from any provider, generate the username, and then save it then DB? I can do it in the createUser event like this:

  events: {
    createUser: async ({user}) => {
      const username = await generateUsername();
      await updateUsername({ userId: user.id, username });
    }
  }

But it seems like events should really be for simple logging and stuff not new DB calls with sideeffects? Plus there is a chance it could fail and then the user wouldn't get a default which could be problematic.