Aggregates (Min, Max) for CharField fails with Postgresql

[wejaay]

If you try to do aggregate on a CharField using with Min or Max, it works fine in sqlite3 but fails in PostgresSQL. I have version 9.0 of postgres and latest dev version of django.

The error occurs because Django is trying to convert the string to float in ​http://code.djangoproject.com/browser/django/trunk/django/db/backends/__init__.py?rev=9742, line number 399.
Thats the version where this code was first introduced and as far as I can tell its been broken all the way from then to most recent version ​http://code.djangoproject.com/browser/django/trunk/django/db/backends/__init__.py, line 553.

One fix that seems to work is to change line 549 from elif internal_type in ('DateField', 'DateTimeField', 'TimeField'): to elif internal_type in ('DateField', 'DateTimeField', 'TimeField', 'CharField'):

I dont know if that has other side effects. If I am doing something wrong, please let me know.

[Russell Keith-Magee]

Marking has-patch because there is a proposed fix, but it needs tests, and needs to be turned into a diff.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Nick Sandford]

I can't reproduce this on Django 1.5b2 and PostgreSQL 9.1.7. It appears convert_values was changed in commit 12a96bfa263d514884ef11009913b2f8bb163472 and this would have fixed the issue.

    In [2]: User.objects.all().aggregate(Max('username'))
    Out[2]: {'username__max': u'test'}