loaddata should allow empty fixtures

[Luc Saffre]

The loading management command does the following test:

# If the fixture we loaded contains 0 objects, assume that an
# error was encountered during fixture loading.
if objects_in_fixture == 0:
    self.stderr.write(
        self.style.ERROR("No fixture data found for '%s'. (File format may be invalid.)\n" %
            (fixture_name)))
    if commit:
        transaction.rollback(using=using)
        transaction.leave_transaction_management(using=using)
    return

I suggest to either remove this test or to add a setting to disable it.
Because a fixture returning no objects is a perfectly possible edge case (depending on some local configuration settings) when using Python fixtures <​http://lino.saffre-rumma.net/topics/dumpy.html>.

[Anssi Kääriäinen]

I don't see any reason why an empty fixture must be an error.

[Renato Oliveira]

I just removed the test. But, if the best way is to create a setting to disable it whenever you want, how would it be?

[Claude Paroz]

I think that at least a warning should be output.

[Renato Oliveira]

Sorry about the delay, I'll send the patch this week.

[Przemek Lewandowski]

Error changed to warning and some updates in tests. ​https://github.com/django/django/pull/799

[Tim Graham]

No longer merges cleanly.

[Tim Graham <timograham@…>]

In 382c53d7d88da70a3645c6db063995382f61dc45:

Fixed #18213 -- Allowed empty fixtures (emit a warning rather than raising an exception).