Adding Autoincrement field to existing model with Django South?

Question

I have a Django project that started as an import of a legacy database. Because of this, there is a model with a composite primary key. This worked as long as I used only the legacy data, but now I want to add new data and the form I created is telling me that I am trying to insert duplicate data, presumably because it is only looking at one of the fields as the primary key.

Now I want to change the model to use an autoincrement primary key, like one Django would automatically add. I tried removing the primary key attributes from the fields and putting them in unique_together in the Meta inner class. When I ran schemamigration with South, it wanted to add an id field as expected, but it asked for a default value.

How can I specify that South should assign unique keys in some way that is reasonable for an autoincrement field? (i.e. assign the sequence [1...n] to some arbitrary ordering of the records)

If this is impossible is there another way to accomplish the same thing, preferably using Django and South?

Answer 1

I solved the problem that required me to do this with a workaround:

I copied the data from the original table into a temporary table in SQL with INSERT INTO... SELECT.... I then deleted the original table and recreated it with the autoincrement field. Then I copied the data back into the new table, with the autoincrement values added automatically by the INSERT command. Finally I executed a fake run of the South migration to make South's tables consistent with the new schema.