Migrating data from “Many-To-Many” to “Many-To-Many Through” in django

Question

I\'ve got a model

class Category(models.Model):
    title           = models.CharField(...)
    entry           = models.ManyToManyField(Entry,null=True,blan         


        

Answer 1

In Django 1.7+ built-in migrations, the way the "code state" (i.e. the code definition of models) is calculated is different, and requires a different solution.

In South (Django pre-1.7), the entire "code state" is saved in each migration — but in Django 1.7+ built-in migrations, it's derived from looking at the whole set of migrations, so you need to specify the "code state" change in a migration without altering the database.

Like above, this will need to be done in a few steps.

1. Create an intermediate model like in the answer above:

   class CategoryEntry(models.Model):
       category = models.ForeignKey(Category, on_delete=models.CASCADE)
       entry = models.ForeignKey(Entry, on_delete=models.CASCADE)   
   
       class Meta:
            db_table = 'main_category_entries'   #change main_ to your application
            unique_together = ('category', 'entry')
   

2. Create an auto-migration with django-admin.py makemigrations and modify the code; move the operations list into the state_operations argument of a migrations.SeparateDatabaseAndState operation, and leave the database_operations list empty. It should look like:

   class Migration(migrations.Migration):
       operations = [
           migrations.SeparateDatabaseAndState(
               state_operations=[ 
                   migrations.CreateModel(CategoryEntry..)
                   ...
               ],
               database_operations=[]
           ),
       ]
   

3. Edit the CategoryEntry to contain what you want and create a new auto-migration with django-admin.py makemigrations