Custom validation in Django admin

Question

I have a very simple Django app in order to record the lectures given my colleagues.Since it is quite elementary,I am using the Django admin itself. Here is my models.py:

#models.py
from django.db import models

class Lecture(models.Model):
    topic = models.CharField(max_length=100)
    speaker = models.CharField(max_length=100)
    start_date = models.DateField()
    end_date = models.DateField()

I need to ensure that nobody enters the start date after the end date in the admin forms,so I read the django docs for custom validation in the admin and implemented the following in my admin.py:

#admin.py
from models import Lecture
from django.contrib import admin
from django import forms


class LectureForm(forms.ModelForm):
    class Meta:
        model = Lecture

        def clean(self):
            start_date = self.cleaned_data.get('start_date')
            end_date = self.cleaned_data.get('end_date')
            if start_date > end_date:
                raise forms.ValidationError("Dates are incorrect")
        return self.cleaned_data


class LectureAdmin(admin.ModelAdmin):
    form = LectureForm
    list_display = ('topic', 'speaker', 'start_date', 'end_date')

admin.site.register(Lecture, LectureAdmin)

However,this has no effect whatsoever on my admin and I am able to save lectures where start_date is after end_date as seen in the image:

What am I doing wrong ??

Answer 1

Usually you just want to define a clean() method on the model itself.

https://docs.djangoproject.com/en/2.1/ref/models/instances/#validating-objects

from django.core.exceptions import ValidationError

class Lecture(models.Model):
    topic = models.CharField(max_length=100)
    speaker = models.CharField(max_length=100)
    start_date = models.DateField()
    end_date = models.DateField()

    def clean(self):
        if self.start_date > self.end_date::
            raise ValidationError("Dates are incorrect")

Something like that will work in the django admin without any need to create a form class.