refactor(UserService): simplify login by using findOrCreate()

[timotheeg]

Problem

Incorrect comments on not being able to use findOrCreate() with a transaction.

(Also I think the old code for create might have been incorrect, because the first argument to create() must be an object, not a string (?) 🤔

While .findOrCreate() does in fact accept a transaction (see API documentation), I think the update to lastLoggedIn doesn't need to be in the transaction. Even if there is a conflict with multiple writes overwriting each other, the updates would be so close by that's the inaccuracy is not business critical.

Because of that, we can simplify the code by using the default transaction behaviour of .findOrCreate(), instead of providing our own transaction.

Solution

1. Use .findOrCreate() in both login and loginWithEmail
2. Move the update to lastLoggedIn out of transaction
3. Update the tests

.findOrCreate() does provide its own transaction, documentation states

If no transaction is passed in the options object, a new transaction will be created internally, to prevent the race condition where a matching row is created by another connection after the find but before the insert call.

Verified on staging (sample trace here):

Tests

• Login successfully via email
• Login successfully via github