Getting ready

Let's suppose that you have the Idea model, with a foreign key pointing to the Category model, as follows:

# demo_app/models.py 
from django.db import models 
from django.utils.translation import ugettext_lazy as _ 
 
class Category(models.Model):
    title = models.CharField(_("Title"), max_length=200)

    def __str__(self):
        return self.title
 
class Idea(models.Model):
    title = model.CharField(
        _("Title"),
        max_length=200)
    category = models.ForeignKey(Category,
        verbose_name=_("Category"),
        null=True,
        blank=True,
        on_delete=models.SET_NULL)
 
    def __str__(self): 
        return self.title 

The initial migration should be created and executed by using the following commands:

(myproject_env)$ python3 manage.py makemigrations demo_app
(myproject_env)$ python3 manage.py migrate demo_app