Optimize callback and change login field on email change

[vinay-mittal]

Issue:
Admin changes email of a user but the login field is not changed for that user. User is able to login only through old email and not able to login through new email of user.

In this callback login field will only be assigned if its nil which means at the time of user creation. On every other case this callback will run and nothing change would happen.
Now, this callback will only run if email is changed and new value of email will be assigned to login.

[krzysiek1507]

I can see another problem. email and login should be unique as a pair. There shouldn't be a way to set the same value for email for user A and login for user B.

[krzysiek1507]

Here this is described.

[vinay-mittal]

@krzysiek1507 if we are having login same as email then the login value will be unique as email is always unique.

[krzysiek1507]

1. By default user can login only using email. If you allow a user to login using login field in your app then you should handle it yourself, but this could be weird to search in 2 columns with same values.
2. I don't think if we should sync login with email.
3. There is a missing index for login field.

[vishalzambre]

@vinay-mittal @krzysiek1507 But then what is the meaning of keeping extra parameter as login.

Its realy good option to have login field separate, It useful in mobile to have mobile number for login parameters.

[vishalzambre]

@damianlegawiec @vinay-mittal @krzysiek1507 We should allow login only using login not by email and as per code self.login ||= email will take care of login should not be null.
Also yes we can add uniq index on both.

[vishalzambre]

If required I can raise PR for uniq index on both.

[kushniryb]

@vinay-mittal Please rebase against master & add some specs. Thanks in advance 👍