How do I migrate models from one app to another with django 1.7 migrations?

[Andy Kish]

Hi gang,

I'm trying to refactor the apps in my project, and I can't figure out any clean way to migrate models with their data from one app to another. I'm really looking for answers to two questions:

1. Is there any canonical way to do this?

2. I've moved my models to the new app but I have them using the tables from the old app using Meta.db_table. How do I make migrations understand what's going on and not try to delete my old tables? Once migrations gets what's going on, how do I rename the old table so it fits the new app name so I no longer need Meta.db_table?

--

For question 1. I'm really surprised there isn't a good way to do this. I mean—this is kind of a blatant use case for a migration—moving a model from one app to another.

My initial thought was to use a use a three phase migration. Create new models, copy data over, delete old models. But I'd really rather not 'cause the models are all very interconnected and that seems like a recipe for a foreign key disaster.

What I actually went with was to move all the models over to the new app, and then point them at the old tables using Meta.db_table. Everything works, but when I run makemigrations it is confused as crap and wants to destroy everything, which brings me to question 2...

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So question 2, now that I have my model code in a new app pointing at the old tables, how do I get the tables renamed to use canonical table names and let migrations know wtf is going on?

With the current situation, if I run makemigrations it does something like this

Migrations for 'new_app':

  0001_initial.py:

    - Create model Building

    ...

    - Add field contact to building

    ...

Migrations for 'old_app':

  0006_auto_delete_blah.py:

    - Remove field contact from building

    ...

    - Delete model Building

    ...

all of which is roughly correct, just doesn't keep my data intact. :P

My gameplan (please correct me if any of this is wrong) is to:

1. Fake the ('new_app', '0001_initial') migration.

2. Make a new data migration depending on ('new_app', '0001_initial') and the ('old_app', '0005_...') that uses AlterModelTable to rename the tables to their canonical names as would normally be created by the 0001_initial migration.

3. Fake the ('old_app', '0006_auto_delete_blah')migration.

4. Get rid of the Meta.db_table entries so my moved models just use the normal table names they're supposed to.

Seems like it should get me to where I want to go.

Am I smoking crack? Is this really that hard?

Thanks!

Andy.

[Collin Anderson]

2. I've moved my models to the new app but I have them using the tables from the old app using Meta.db_table. How do I make migrations understand what's going on and not try to delete my old tables? Once migrations gets what's going on, how do I rename the old table so it fits the new app name so I no longer need Meta.db_table?

Autodetecting changes to Meta.db_table was just added in django 1.7.1, so try that out if you haven't.