Django NullCharField subclass of the CharField that allows empty strings to be stored as NULL in database

null_char_field.py

from django.db.models import CharField
from django.core.exceptions import ImproperlyConfigured
from django.utils.translation import ugettext_lazy as _


class NullCharField(CharField):
    """
    Subclass of the CharField that allows
    empty strings to be stored as NULL in database
    """
    description = _("CharField that stores '' as None and returns None as ''")

    def __init__(self, *args, **kwargs):
        if not kwargs.get('null', True) or not kwargs.get('blank', True):
            raise ImproperlyConfigured(
                'NullCharField implies null==blank==True')
        kwargs['null'] = kwargs['blank'] = True
        super().__init__(*args, **kwargs)

    def to_python(self, value):
        val = super().to_python(value)
        return '' if val is None else val

    def get_prep_value(self, value):
        prep_value = super().get_prep_value(value)
        return None if prep_value == '' else prep_value

    def deconstruct(self):
        """
        For migration purposes
        """
        name, path, args, kwargs = super().deconstruct()
        del kwargs['null']
        del kwargs['blank']
        return name, path, args, kwargs