How to set `null=True` for a field using `label_from

I am trying to set null=True and blank=True for a field using label_from_instance.

But it cannot be set by defining a field in the model class.

If I try to set it like the code below, I get an error.

fk_id = NameChoiceField(queryset=PkModel.objects.all().order_by('pk_name').distinct(), null=True, blank=True)

TypeError: init() got an unexpected keyword argument 'null'

How could I set null and blank in this case?

Here are the codes:

forms.py

from django import forms
from django.forms import ModelChoiceField

from .models import *


class NameChoiceField(ModelChoiceField):

    def label_from_instance(self, obj):
        return f'{obj.pk_name}'


class IndexForm(forms.ModelForm):
    fk_id = NameChoiceField(queryset=PkModel.objects.all().order_by('pk_name').distinct())

    class Meta:
        model = FkModel
        fields = '__all__'

models.py

from django.db import models


class PkModel(models.Model):
    pk_id = models.IntegerField(verbose_name='pk_id',primary_key=True)
    pk_name = models.CharField(max_length=20, verbose_name='pk_name')

    class Meta:
        verbose_name_plural = 'PkModel'


class FkModel(models.Model):
    fk_code = models.CharField(max_length=20, verbose_name='fk_code', primary_key=True)
    fk_id = models.ForeignKey(PkModel, to_field='pk_id', db_column='fk_id', verbose_name='fk_id',
                                on_delete=models.CASCADE, null=True, blank=True)

    class Meta:
        verbose_name_plural = 'FkModel'

Python 3.8

Django 3.2

CodePudding user response：

Use required=False.

null and blank are for model fields, and describe valid data at the database level. In a form, you instead declare whether the field must be set for the form to be valid.