CODEWITHSUNDEEP
pythondjangodjango-modelsdatabase-migrationdjango-south
funkotron
funkotron

Reputation: 407

Django Data Migration, using South with Inheritance

We are migrating the data in several instances of our Django project to a new schema.

The old schema had:

class Group(models.Model)
class User(models.Model)

And the new schema has:

class AccessEntity(models.Model)
class Group(AccessEntity)
class User(AccessEntity)

We are trying to use South to do a data migration for these groups and users. http://south.aeracode.org/docs/tutorial/part3.html

I've gathered that I'll need to use forward rules to specify how to migrate the Users but there are a few issues I've run up against.

The main issue is how to keep the ID of the User/Group the same if I were to create a new User object that extends the AccessEntity class.

Users & Groups are referenced to by objects they own or are assigned to them. If I change their ID that information would be lost. Is there a way of keeping the same ID for an object even though I need it to now extend from AccessEntity?

Upvotes: 0

Views: 1353

Answers (1)

Paul
Paul

Reputation: 8182

not sure if I understand your question correctly, but the way multi-table model inheritance works ist that there will be an implicit one-to-one field in the parent and child models. So both User and Group would use an ID field of AccessEntity if AccessEntity has such a field.

If you create AccessEntity such that it has a field ID you can assign to it when you write a forward (data)-migration. That way you can make sure that the AccessEntity gets the right ID.

If have written a longer multi-table inheritance tutorial and it looks like you are trying to do something similar.

And furthermore the answer to this question could also be helpful (note that some things in the original answer does will not work in new versions of django / south, see my tutorial / the answer at the bottom for changes).

What might be a problem in your case is that if you already have data in both User and Groups and the id field is auto-generated, IDs likely not be distinct, e.g. you are likely going to have both a User and a Group with ID==1. This could be a problem if you want to query based on those IDs and of course ID could not be a primary key for AccessEntity then.

Upvotes: 2

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