Add non-null and unique field with already populated model
Unfortunatelly, I found no answer but I could create one solution:
- First I have created a migration that allows the slug field to be nullable;
- Then I have created another migration that populates the slug column with proper values to every row in the model;
- Then another migration which adds the not-null constraint in the column.
You do your model changes (add field, change, etc), then you call manage.py makemigrations, then apply the migrations with manage.py migrate
You can add the field with null=True, then you e.g. make a script to populate it one time
Otherwise, if you need to populate the field within the migration you can write a custom one, see https://docs.djangoproject.com/en/1.7/ref/migration-operations/#writing-your-own