Using Django's new migration framework, let's say I have the following model that already exists in the database:
class TestModel(models.Model):
field_1 = models.CharField(max_length=20)
I now want to add a new TextField to the model, so it looks like this:
class TestModel(models.Model):
field_1 = models.CharField(max_length=20)
field_2 = models.TextField(blank=True)
When I try to migrate this model using python manage.py makemigrations, I get this prompt:
You are trying to add a non-nullable field 'field_2' to testmodel without a default; we can't do that (the database needs something to populate existing rows).
Please select a fix:
1) Provide a one-off default now (will be set on all existing rows)
2) Quit, and let me add a default in models.py
I can easily fix this by adding null=True to field_2, but Django's convention is to avoid using null on string-based fields like CharField and TextField (from https://docs.djangoproject.com/en/dev/ref/models/fields/). Is this a bug, or am I misunderstanding the docs?
It's not a bug, it's documented and logical.
You add a new field, which is (by best practice, as you noticed) not NULLable so django has to put something into it for the existing records - I guess you want it to be the empty string.
you can
1) Provide a one-off default now (will be set on all existing rows)
so just press 1, and provide '' (the empty string) as value.
or specify default='' in the models.py, as suggested:
2) Quit, and let me add a default in models.py