How to avoid race condition with unique checks in Django

Question

I have a simple model:

class InvitationRequest(models.Model):
    email = models.EmailField(max_length=255, unique=True)
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Answer 1

The standard way is to NOT handle this, as:

1. the probability of the failure in your case is close to 0;
2. the severity of the failure is very low.

If, for some reason, you have to be sure that the problem won't happen, you are on your own.

I haven't analyzed the sequence of events in detail but I think that using the SERIALIZABLE isolation level won't really help, it will only cause IntegrityError (or DatabaseError) to be raised in a different place.

Overriding Model._perform_unique_checks sounds to me like a bad idea, you better stay away from monkey patching if possible (and here it is possible).

As for using the table lock to prevent unlikely errors... Well, I'm not a big fan so I cannot recommend that either.

Here's a nice answer to a similar question: https://stackoverflow.com/a/3523439/176186 - I concur that catching IntegrityError and retrying is probably the easiest sane way to deal with the problem.

EDIT: I found this: Symfony2 - how to recover from unique constraint error after form submission? and I agree with @pid's answer.