Catching errors inside transaction.atomic()

[Alex Krupp]

The Django documentation gives a warning to avoid catching errors inside transaction.atomic() blocks, and to use nested transactions if you need to do so. But in the case where we have code like:

with transaction.atomic():
    # Create and save some models here

    try:
        SomeModel.objects.get(id=NON_EXISTENT_ID)
    except SomeModel.DoesNotExist:
        raise SomeCustomError()

Will anything bad actually happen if we just immediately raise a custom error without doing any other error handling? The expected behavior in this case would be that the entire transaction gets rolled back, and so nothing before or after the exception is committed.

I'm just wondering in cases like these there is any reason for using the recommended nested transaction, or if it's just extra code that's not serving any purpose. The examples only speak to cases where there is there would otherwise be database queries getting executed in between the first database error and the end of the transaction, which isn't the case here.

[Jani Tiainen]

Catching errors inside transaction might lead inconsistent state if the database if error handling swallows exception.

Reraising exception or like you want to do raise new exception it would work as expected.

Nested atomic blocks can be used to safely rollback state of database if you want to handle smaller units of transactiond.

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