id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
22536	Exceptions using date-based generic views with MySQL, USE_TZ=True and bad data	Chris Adams	Chris Adams	"I ran into a non-obvious exception while using the date-based generic views. get_previous_day / get_next_day were raising an AttributeError ('NoneType' object has no attribute 'astimezone') in the following code when the view was called with the earliest item in the system:

{{{
        try:
            result = getattr(qs[0], date_field)
        except IndexError:
            return None

        # Convert datetimes to dates in the current time zone.
        if generic_view.uses_datetime_field:
            if settings.USE_TZ:
                result = timezone.localtime(result)
            result = result.date()
}}}

This error wasn't immediately obvious because the query shouldn't have been able to return a NULL. Looking at the data revealed the problem: a small number of records on my test instance had invalid dates in MySQL (0000-00-00) which were included by the __lt query but subsequently converted into None by the ORM. 

The nature of the bug suggests that the cleanest patch might simply be an immediate ""if not result: return None"", perhaps with a warning about invalid data."	Bug	new	Generic views	1.5	Normal				Accepted	0	0	0	0	0	0