Cannot bypass 'Duplicate Username' Salesforce error on before insert User Trigger

Question

As per standard functionality, when one tries to create/update a user record with a username value that is NOT unique across all Salesforce orgs, then the following error message is returned:

Duplicate Username.
The username already exists in this or another Salesforce organization. Usernames must be unique across all Salesforce organizations. To resolve, use a different username (it doesn't need to match the user's email address).

I tried to bypass this with a before insert User trigger to say 'if any DML exception is hit, then append a value to the username' such that one wouldn't hit such errors.

I created the most granular debug log level but I don't see any DML exception or any other 'hook' that I could use for this.

It would seem that this exception is just not available to developers in any logs. Is this correct?

Answer 1

Correct, you cannot catch this error in a trigger. This error occurs before any triggers are executed. This is true for all standard validations, such as DUPLICATE_VALUE, REQUIRED_FIELD_MISSING, etc.