CODEWITHSUNDEEP
djangomigrationdjango-south
paldepind
paldepind

Reputation: 4870

How to create new field in a model with initial data from another field?

In my Django app I have a model like the following:

class Foo(models.Model):
  ...
  user = models.OneToOneField(User)
  ...

Here user is from django.contrib.auth.models. I'm using South for migrations and I want to extend Foo with a new boolean field with the initial data equal to the is_active field in in the User model contained in Foo's user field.

Upvotes: 0

Views: 81

Answers (1)

falsetru
falsetru

Reputation: 369124

Use Data migrations

  1. Do a schema migration first: add is_active field to Foo class.

    # edit your appnames/models.py
python manage.py schemamigration appname --auto 
python manage.py migrate appname

  2. Do a data migration:

    $ python manage.py datamigration appname copy_is_active

  3. Edit appname/migrations/0???_copy_is_active.py, especially forwards method to do what you want.

    For example,

    ....
from appname.models import Foo

class Migration(DataMigration):
    def forwards(self, orm):
        for obj in Foo.objects.all():
            obj.is_active = obj.user.is_active
            obj.save()
        #for yn in (True, False):
        #    Foo.objects.filter(user__is_active=yn).update(is_active=yn)
...

  4. Execute the migration

    $ python manage.py migrate appname

Upvotes: 2

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