How can I implement validation in Django admin?

How can I implement validation in Django admin?

You can implement validation in Django admin by overriding the clean method in your model admin class.

Can you give me an example of how to override the clean method?

Sure! Here's a simple example:

from django.contrib import admin
from .models import MyModel

class MyModelAdmin(admin.ModelAdmin):
    def clean(self, obj):
        if obj.some_field < 0:
            raise ValidationError('Value cannot be negative.')
        super().clean(obj)

admin.site.register(MyModel, MyModelAdmin)

What if I want to add custom error messages?

You can customize error messages by passing a message string to the ValidationError like this:

raise ValidationError('Custom error message here.')