A migration like this needs to be done in a few distinct migrations.
Here is a nice example from the south tutorial:
http://south.aeracode.org/docs/tutorial/part3.html#data-migrations
For your example you will probably need to perform these distinct
actions:
- add tagging_tags
- migrate data to tagging_tags
- rename tagging_tags to tags.
1) Add TagField to Tour model and create schemamigration.
class tour(models.Model):
# ...
tagging_tags = TagField() # will rename to tags later
./manage.py schemamigration tour --auto
2) Migrate from Tag to TagField.
./manage.py datamigration tour switch_from_tags_to_tagging_tags
# 000x_switch_from_tags_to_tagging_tags.py
def forwards(self, orm):
for tour in orm.Tour.objects.all():
old_tags = ",".join([tag.name for tag in tour.tags.all()])
tour.tagging_tags = old_tags
tour.save()
3) Rename the TagField column to tags.
# delete the Tag class and tweak Tour class
class Tour(models.model):
# ...
tags = TagField() # was tagging_tags
./manage.py schemamigration tour --auto
# 000x_auto__del_tag[...].py
def forwards(self, orm):
# ... replace the del_column tagging_tags and add_column tags
w/
# Renaming field 'Tour.tagging_tags' to 'Tour.tags'
db.rename_column('tours_tour', 'tagging_tags', 'tags')
Best,
Ian
On Apr 11, 5:06 am, Andrey Torba <andreyto...@gmail.com> wrote:
> Hi all,
> --------
> There are simple model and tag:
> --------
> class Tag(models.Model):
> name = models.CharField(max_length=50)
>
> class Tour(models.Model):
> name = models.CharField(max_length=50)
> tags = models.ManyToManyField('Tag',
> related_name='tours',)
>
> --------
> I want refactor data base to use django-tagging.
> --------
> class Tour(models.Model):
> name = models.CharField(max_length=50)
> tags = models.ManyToManyField('Tag',
> related_name='tours',)
>
> import tagging
> tagging.register(Tour)
>
> --------
> First i do datamigration:
> --------
> ./manage.py datamigration --freeze=tagging tour migrate_to_tagging
>
> --------
> Here i shold implement 'forward' and 'backward' methods.
> How to do it? My wrong variant:
> --------
> class Migration(DataMigration):
>
> def forwards(self, orm):
> for tag in orm.Tag.objects.all():
> for tour in tag.tours.all():
> orm['tagging.Tag'].objects.add_tag(tour, tag.name)
>
> def backwards(self, orm):
> for tag in orm['tagging.Tag'].objects.all():
> for tour in tag.tours.all():
> tour.tags.add(tag.name)
>
> --------
> This is wrong:
> --------
> orm['tagging.Tag'].objects.add_tag(tour, tag.name)
>
> AttributeError: 'Manager' object has no attribute 'add_tag'
>
> --------
> How to migrate data in right way
>
> --
> Regards, Andrey
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