Migrations - moving model between apps

[Matthew Pava]

I’m moving a model to a different app in my project, and I want to keep the same data that I already have.  I created a migration with a RunSQL operation that simply renames the table with the new app prefix.  However, when I run makemigrations, Django insists on adding a migrations.CreateModel operation for me in the new app.  How do I avoid that?

[Simon Charette]

Hello Matthew,

I'm going to assume no foreign keys are pointing to the model "Foo" you are

trying to move from the app "old" to "new". If it's the case then simply repoint

them and run makemigrations once the following steps are completed. You

could wrap the generated AlterField in SeparateDatabaseAndState to avoid

database level foreign key constraints reconstruction if it's critical to your

application.

Start by setting old.Foo.Meta.db_table = 'new_foo' and run makemigrations old.

That should generate you a new migration with an AlterModelTable('foo', 'new_foo') operation.

Within this migration you'll want to add a DeleteModel('foo') operation wrapped in a

SeparateDatabaseAndState[0] after the AlterModelTable one. Your migration's operations

should look like:

operations = [

    AlterModelTable('foo', 'new_foo'),
    SeparateDatabaseAndState([], [DeleteModel('foo')]),

]

Now, move your "old.Foo" model definition to your "new" app, remove the

new.Foo.Meta.db_table and run "makemigrations new".

Edit the created "new" migration and wrap the CreateModel into a SeparateDatabaseAndState

and make sure the migration depends on the "old" migration you just created. You migration

should look like the following:

dependencies = [

    ('old', '000N_old_migration_name'),

]

operations = [

    SeparateDatabaseAndState([], [

        CreateModel('foo, ...)

    )]),

]

Note that this will not take care of renaming the content types and permissions that

might have been created for your old.Foo model definition. You could use a RunPython

operation to rename them appropriately.

Cheers,

Simon

[Matthew Pava]

Hi Simon,

Thank you so very much for your assistance.

It was a very simple model, so it had no foreign keys, and I’m relieved that I won’t have to do some manual database operations to get this working.

It has migrated successfully!

Thank you,

Matthew

--
You received this message because you are subscribed to the Google Groups "Django users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to django-users...@googlegroups.com.
To post to this group, send email to django...@googlegroups.com.
Visit this group at https://groups.google.com/group/django-users.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/20606f64-15b4-4946-bb3e-65276de63e40%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.