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
21312	models.DateTimeField with default=now: South migration fails	Mathieu Agopian	nobody	"This is a problem that didn't happen on django1.6b4, but does on django1.6c1:

Here's a snippet of the model:


{{{
from django.utils.timezone import now


@python_2_unicode_compatible
class User(AbstractBaseUser, PermissionsMixin):
    """"""TopChretien User, identified by its email.""""""
    ...
    last_modified = models.DateTimeField(
        _('last modification'), default=now, editable=False)
    ...
}}}

Here's the auto migration created by South when adding this new field to the model:

{{{
import datetime
...

class Migration(SchemaMigration):

    def forwards(self, orm):
        # Adding field 'User.last_modified'
        db.add_column(u'user_user', 'last_modified',
                      self.gf('django.db.models.fields.DateTimeField')(default=datetime.datetime.now),
                      keep_default=False)
}}}

And here's the result of running ""manage.py migrate user"" on django1.6b4:

{{{
$ ./manage.py migrate user
Running migrations for user:
 - Migrating forwards to 0007_auto__add_field_user_last_modified__add_field_user_moderation_date__ad.
 > user:0007_auto__add_field_user_last_modified__add_field_user_moderation_date__ad
/home/mathieu/.virtualenvs/top/lib/python2.7/site-packages/django/db/models/fields/__init__.py:901: RuntimeWarning: DateTimeField received a naive datetime (2013-10-23 15:50:11.448018) while time zone support is active.
  RuntimeWarning)

 - Loading initial data for user.
Installed 0 object(s) from 0 fixture(s)
}}}

And now on django1.6c1 (only the end of stacktrace, for readability, please let me know if you need more):

{{{
  File ""/home/mathieu/Dropbox/dev/topchretien/web/topchretien/user/migrations/0007_auto__add_field_user_moderation_date__add_field_user_moderator__add_fi.py"", line 14, in forwards
    keep_default=False)
  File ""/home/mathieu/.virtualenvs/top/lib/python2.7/site-packages/south/db/generic.py"", line 47, in _cache_clear
    return func(self, table, *args, **opts)
  File ""/home/mathieu/.virtualenvs/top/lib/python2.7/site-packages/south/db/generic.py"", line 411, in add_column
    sql = self.column_sql(table_name, name, field)
  File ""/home/mathieu/.virtualenvs/top/lib/python2.7/site-packages/south/db/generic.py"", line 706, in column_sql
    default = field.get_db_prep_save(default, connection=self._get_connection())
  File ""/home/mathieu/.virtualenvs/top/lib/python2.7/site-packages/django/db/models/fields/__init__.py"", line 350, in get_db_prep_save
    prepared=False)
  File ""/home/mathieu/.virtualenvs/top/lib/python2.7/site-packages/django/db/models/fields/__init__.py"", line 911, in get_db_prep_value
    value = self.get_prep_value(value)
  File ""/home/mathieu/.virtualenvs/top/lib/python2.7/site-packages/django/db/models/fields/__init__.py"", line 902, in get_prep_value
    (self.model.__name__, self.name, value),
AttributeError: 'DateTimeField' object has no attribute 'model'
}}}


The solution I used was to modify the South migration to get rid of the warning (in Django1.6b4) and make it work correctly (in django1.6c1):

{{{
import django.utils.timezone
...

class Migration(SchemaMigration):

    def forwards(self, orm):
        # Adding field 'User.last_modified'
        db.add_column(u'user_user', 'last_modified',
                      self.gf('django.db.models.fields.DateTimeField')(default=django.utils.timezone.now),
                      keep_default=False)
}}}"	Uncategorized	closed	Database layer (models, ORM)	1.6-beta-1	Normal	invalid		pronik	Unreviewed	0	0	0	0	0	0