Django 1.8: Delete/rename a model field in data migration

Question

I need to change the relationship of a model field from ForeignKey to ManyToManyField. This comes with a data migration, to update the pre-existing data.

The following is the original model (models.py):

class DealBase(models.Model):

    [...]
    categoria = models.ForeignKey('Categoria')
    [...]

    )

I need the model field 'categoria' to establish a many2many relationship with the model 'Categoria' in the app 'deal'.

What I did:

1. Create a new field 'categoria_tmp' in DealBase

   class DealBase(models.Model):
        categoria = models.ForeignKey('Categoria')
        categoria_tmp = models.ManyToManyField('Categoria',related_name='categoria-temp')
   

2. make a schema migration

   python manage.py makemigrations

3. Edit the migrationfile.py to migrate data from categoria to categoria-tmp

   def copy_deal_to_dealtmp(apps, schema_editor):
       DealBase = apps.get_model('deal', 'DealBase')
   
       for deal in DealBase.objects.all():
           deal.categoria_tmp.add(deal.categoria)
           deal.save()
   
   class Migration(migrations.Migration):
   
       dependencies = [
         ('deal', '0017_dealbase_indirizzo'),
       ]
   
       operations = [
          migrations.AddField(
          model_name='dealbase',
          name='categoria_tmp',
          field=models.ManyToManyField(related_name='categoria-temp', to='deal.Categoria'),
          preserve_default=True,
         ),
   
          migrations.RunPython(
           copy_deal_to_dealtmp
          )
         ]
   

4. make data migration

   python manage.py migrate

5. Finally I need to delete the column 'dealbase.categoria' and rename the column 'dealbase.categoria-tmp' to 'dealbase.categoria'

I'm stuck at step 5.

Could someone help me out? I cannot find online an answer, I'm using Django 1.8.

Thanks!

Solution

You just need to create two additional migrations: one to remove the old field and the other to alter the new field.

First remove dealbase.categoria and create a migration and then rename dealbase.categoria-tmp to dealbase.categoria and create another migration.

This will delete the first field and then alter the tmp field to the correct name.

Comments

[user123892]

Thank you for your answer. I did as Jeff_Hd suggested and it worked. I'm sure your solution is also a valid one. If @Jeff_Hd does not make an answer from his comment, I will give the 'solved' to yours.

[itzMEonTV]

No, please accept the answer which solved your problem. I am not at all sure this is best answer.If Jeff_Hd's answer solved yours, accept it.

[bruno desthuilliers]

For anyone reading ths answer : steps 2 and 5 are plain wrong, you want data migrations instead.

[Sido4odus]

Does Django execute operations in order (sequentially) ?