Showing custom model validation exceptions in the Django admin site

Question

I have a booking model that needs to check if the item being booked out is available. I would like to have the logic behind figuring out if the item is available centralised so that no matter where I save the instance this code validates that it can be saved.

At the moment I have this code in a custom save function of my model class:

def save(self):     if self.is_available(): # my custom check availability function         super(MyObj, self).save()     else:         # this is the bit I'm stuck with..         raise forms.ValidationError('Item already booked for those dates') 

This works fine - the error is raised if the item is unavailable, and my item is not saved. I can capture the exception from my front end form code, but what about the Django admin site? How can I get my exception to be displayed like any other validation error in the admin site?

Answer 1

In django 1.2, model validation has been added.

You can now add a "clean" method to your models which raise ValidationError exceptions, and it will be called automatically when using the django admin.

The clean() method is called when using the django admin, but NOT called on save().

If you need to use the clean() method outside of the admin, you will need to explicitly call clean() yourself.

http://docs.djangoproject.com/en/dev/ref/models/instances/?from=olddocs#validating-objects

So your clean method could be something like this:

from django.core.exceptions import ValidationError  class MyModel(models.Model):      def is_available(self):         #do check here         return result      def clean(self):         if not self.is_available():             raise ValidationError('Item already booked for those dates') 

I haven't made use of it extensively, but seems like much less code than having to create a ModelForm, and then link that form in the admin.py file for use in django admin.