Django model select between two columns/fields? - django

Question

I have a Slider module that i want to include items from movies_movie and shows_show table. An item can either be a show or movie. How do i make user select between movie and show? Currently i have columns for movie and show but how do i force user to select between the two?
also title_en is a column in movie or tv show tables. So the title of the movie/show selected should display in row after save.
class Slider_items(models.Model):
order = models.IntegerField(max_length=3, blank=True)
movie = models.ForeignKey('movies.movie', on_delete=models.CASCADE, blank=True)
show = models.ForeignKey('shows.show', on_delete=models.CASCADE, blank=True)
def __str__(self):
return self.title_en
class Meta:
verbose_name = "Slider Items Module"
verbose_name_plural = "Slider Item Module"
Also if a show is selected and a movie isn't, how do i know title_en will be taken from show and not movie?

Answer 1

I think you can do something like this:
from django.core.exceptions import ValidationError
from django.utils.translation import ugettext_lazy as _
class Slider_items(models.Model):
order = models.IntegerField(max_length=3, blank=True)
# don't forget to add null=True to both fields
movie = models.ForeignKey('movies.movie', on_delete=models.CASCADE, blank=True, null=True)
show = models.ForeignKey('shows.show', on_delete=models.CASCADE, blank=True, null=True)
# see docs, https://docs.djangoproject.com/en/3.2/ref/models/instances/#django.db.models.Model.clean
def clean(self):
if self.movie and self.show:
raise ValidationError({'movie': _('You can't select both types at the same time')})
elif not self.movie and not self.show:
raise ValidationError({'movie': _('You must select one type')})
def __str__(self):
return self.movie.title_en if self.movie else self.show.title_en
class Meta:
verbose_name = "Slider Items Module"
verbose_name_plural = "Slider Item Module"

Answer 2

You may consider using django contenttypes.
Imagine in the future, you have not just Movie, Show, but have new Class such as Book, Podcase, it might not be a good idea to keep adding new foreignkey to your Slider Model.
I have not used contenttype before, so I am referencing this SO answer.
(using python 3.6, django 3.2)
models.py
from django.db import models
from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType
class Movie(models.Model):
title = models.CharField(max_length=50)
director = models.CharField(max_length=50)
class Show(models.Model):
title = models.CharField(max_length=50)
date = models.DateField()
class Slider(models.Model):
order = models.IntegerField(max_length=3, blank=True)
choices = models.Q(model='movie') | models.Q(model='show')
selection_type = models.ForeignKey(
ContentType, limit_choices_to=choices,
on_delete=models.CASCADE)
selection_id = models.PositiveIntegerField()
selection = GenericForeignKey('selection_type', 'selection_id')
def __str__(self):
return self.selection.title
admin.py
#admin.register(Slider)
class SliderAdmin(admin.ModelAdmin):
pass
at django shell, the following is valid.
movie = Movie.objects.create(title='movie 1', director='ben')
show = Show.objects.create(title='show 1', date='2021-01-01')
s1 = Slider.objects.create(selection=movie, order=1)
s2 = Slider.objects.create(selection=show, order=2)
However, using limit_choices_to only restrict the choices in admin page, and there is no constraint at database level. i.e. the following are actually legal.
place = Place.objects.create(name='home')
s3 = Slider.objects.create(selection=s3, order=3)
I have not found a fix for this issue yet. Maybe doing some validation in save method is a way (see the comments under this).