"This field may not be null." for models.CharField declared with blank=True about wq.db HOT 2 CLOSED

Yes, this is a bug in wq.db's ModelSerializer, which converts all incoming "" to None before running the validation. A temporary workaround would be to create a custom ModelSerializer that restores the blank value:

# myapp/serializers.py
from wq.db.rest.serializers import ModelSerializer

class MyModelSerializer(ModelSerializer):
    def to_internal_value(self, data):
        result = super().to_internal_value(data)
        if result.get('fieldname', None) is None:
            result['fieldname'] = ""
        return result

# myapp/rest.py
from wq.db import rest
from .serializers import MyModelSerializer
from .models import MyModel

rest.router.register_model(
    MyModel,
    serializer=MyModelSerializer,
)

The longer term fix is a bit more complicated. The issue narrows down to the fact that wq.db's ModelSerializer uses the HTML JSON Forms parser to handle potentially nested records. This processing happens early, so that by the time the validators run, the data is treated as if it had been submitted via a JSON API. Since JSON differentiates between null and "", but HTML does not, I had to make an arbitrary decision how to handle empty strings when converting from an HTML Form submission to JSON (see this function). I chose to treat all empty strings as null, since that was the more common interpretation in my usage. The downside is that blank=True doesn't work at all.

Django REST Framework itself does not suffer from this constraint, because it has access to both the field properties and the structure of the input data at the same time (see this function). When is_html_input() is run on a dictionary that has already been processed by HTML JSON forms, it returns False, so the allow_blank handling code doesn't run.

If you aren't using nested serializers you technically don't need HTML JSON Forms at all, though I don't currently have an easy way to disable the functionality.

from wq.db.

Another workaround: I noticed that if I set value of these non-nullable text fields to " " (a space), they are stored in the database as empty strings (without conversion to NULL).

from wq.db.