How can I allow django admin to set a field to NULL?

I've set my Model field to null=True, which allows NULL in MySQL, but I can't seem to assign NULL to the field through Django Admin. I've tried also setting blank=True, but that just sets the field to an empty string. Following this didn't work either, as the field value was set to "None", the string.

Any ideas?

Try to overwrite the save() method of the Model, to check for empty values:

class MyModel(models.Model):

    my_nullable_string = models.CharField(max_length=15, null=True, blank=True)

    def save(self, *args, **kwargs):
         if not self.my_nullable_string:
              self.my_nullable_string = None
         super(MyModel, self).save(*args, **kwargs)

This section in the docs makes it sound like you can't set a string-based field to NULL through the admin; it will use the empty string. This is just the way Django does it. It will work for other types of fields.

You'll either have to hack on the admin script or else decide it doesn't really need to be NULL in the database; an empty string is OK.

try this code, here Language.subregion hass null=True this code overwrites admin form settings (LanguageAdmin) and sets "subregion" field property - required to False

from app.models import Language
from django.contrib import admin

class Language(models.Model):
    subregion = models.ForeignKey(SubRegion, null=True)
    code = models.CharField(max_length=10, unique=True)

class LanguageAdmin(admin.ModelAdmin):

    def get_form(self, request, obj=None, **kwargs):
        form = super(LanguageAdmin, self).get_form(request, obj, **kwargs)
        form.base_fields['subregion'].required = False
        return form

admin.site.register(Language, LanguageAdmin)

Usually, when you pass both null=True and blank=True, if you leave the field blank in the admin, Django will use NULL for its value.

EDIT:

as agf explains in his answer, this is true for all types except CharField and TextField.

I often use Django just for the Admin and need to preserve a lot of NULLs in the db. I use this snippet to set all empty strings on a particular object to NULL.

def save(self, *args, **kwargs):
    for var in vars(self):
        if not var.startswith('_'):
            if self.__dict__[var] == '':
                self.__dict__[var] = None
    super(MyModel, self).save(*args, **kwargs)

Note that this is fixed in Django 2.0.1 -- from that version on, empty values will be saved as None for nullable Charfields.

Ticket: https://code.djangoproject.com/ticket/4136

Commit: https://github.com/django/django/commit/267dc4adddd2882182f71a7f285a06b1d4b15af0