Default value of DateTimeField for South migration

问题:

I'm creating a schema migration with South 0.7.6 for my Django 1.4.3 project with enabled timezone support.

The schema migration includes adding a DateTimeField (with auto_now=True) on one table.

When creating the migration, South prompts me:

The field 'MyTable.my_field' does not have a default specified, yet is NOT NULL.
Since you are adding this field, you MUST specify a default
value to use for existing rows. Would you like to:
 1. Quit now, and add a default to the field in models.py
 2. Specify a one-off value to use for existing columns now

What's the correct one-off value to give here, if I don't care about this value for existing rows (I just want the migration to succeed without warnings)?

So far, I used datetime.datetime.utcnow(). However, then I get the following when applying the migration:

C:\Python27\lib\site-packages\django\db\models\fields\__init__.py:808:
RuntimeWarning: DateTimeField received a naive datetime (2013-01-16 00:00:00)
while time zone support is active.

South does not seem to import pytz or the Django helper classes, so how can I give a timezone-aware default value here?

回答1:

Manually edit the migration file that South created and add:

from django.utils import timezone

Then find the field that you are adding in the migration file and set its default to timezone.now().

回答2:

pytz can be used for making timezone-aware datetime objects. you can use the following in your migration file:

import pytz
cn_tz = pytz.timezone('Asia/Shanghai')

then in your model

self.gf('django.db.models.fields.DateTimeField')(auto_now=True, default=datetime.datetime.now(cn_tz), blank=True),

回答3:

I noticed when I ran migrations on dev machine, it was different than when I ran them on production.

My dev machine at the top of the file has

    from south_utils import datetime_utils as datetime

where on production it generated

    import datetime

By replacing the latter with the former, it solved my issue with no additional edits to the migration file.