from django.db import models
from django.db import migrations
from django.utils import timezone


def fill_publication_date(apps, schema_editor):
    Entry = apps.get_model('zinnia', 'Entry')
    for entry in Entry.objects.all():
        entry.publication_date = entry.creation_date
        entry.save()


def unfill_publication_date(apps, schema_editor):
    pass


class Migration(migrations.Migration):

    dependencies = [
        ('zinnia', '0002_lead_paragraph_and_image_caption'),
    ]

    operations = [
        migrations.AlterModelOptions(
            name='entry',
            options={
                'ordering': ['-publication_date'],
                'get_latest_by': 'publication_date',
                'verbose_name': 'entry',
                'verbose_name_plural': 'entries',
                'permissions': (('can_view_all', 'Can view all entries'),
                                ('can_change_status', 'Can change status'),
                                ('can_change_author', 'Can change author(s)'))
            }
        ),
        migrations.AddField(
            model_name='entry',
            name='publication_date',
            field=models.DateTimeField(
                default=timezone.now,
                help_text="Used to build the entry's URL.",
                verbose_name='publication date',
                db_index=True),
        ),
        migrations.AlterField(
            model_name='entry',
            name='creation_date',
            field=models.DateTimeField(
                default=timezone.now,
                verbose_name='creation date'),
        ),
        migrations.AlterField(
            model_name='entry',
            name='slug',
            field=models.SlugField(
                help_text="Used to build the entry's URL.",
                max_length=255,
                verbose_name='slug',
                unique_for_date='publication_date'),
        ),
        migrations.AlterIndexTogether(
            name='entry',
            index_together=set([
                ('slug', 'publication_date'),
                ('status', 'publication_date',
                 'start_publication', 'end_publication')]),
        ),
        migrations.RunPython(fill_publication_date, unfill_publication_date)
    ]

Add migration for publication_date field
Add migration for publication_date field
