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How to add one to one relation field in a existing model through South migration

I already have a model,

class ModelA( models.Model ):
    name = models.CharField ( max_length = 255, blank = False )

and i have many entries in it. Now i want to add a field in it, which is

user = models.OneToOneField( User )

How do i add this field into ModelA? Is there any solution other than deleting all previous entries?

like image 727
Ahsan Avatar asked Dec 21 '11 08:12

Ahsan


1 Answers

I would use this pattern:

  1. Add "user = models.OneToOneField(User, null=True)" to your Model (don't remove the "name" field)
  2. run 'manage.py schemamigration --auto'. And apply the migration. Now there are two columns in your table.
  3. Now create a datamigration. Edit the file: you need to loop over all objects in your model and set the user field.
  4. Remove the "name=models.CharField" from the model.py file. And remove the null=True from the user field.
  5. run 'manage.py schemamigration --auto'. And apply the migration

BTW, if you use OneToOneField() without null=True, you can set primary_key=True on this field, since it must be unique. But I don't know if south can handle this migration.

like image 84
guettli Avatar answered Sep 28 '22 16:09

guettli