Django override the error message that Django shows for UniqueConstraint error?

Question

I want to customize Meta class constraints default message. Here is my model that I have been working out.

class BusRoute(BaseModel):
    route = models.ForeignKey(Route, on_delete=models.PROTECT)
    shift = models.ForeignKey(
        Shift,
        null=True,
        on_delete=models.PROTECT
    )
    journey_length = models.TimeField(null=True)
    

    class Meta:
        default_permissions = ()
        verbose_name = 'Bus  Route'
        verbose_name_plural = 'Bus  Routes'
        constraints = [
            models.UniqueConstraint(
                fields=['route', 'shift'],
                name='unique_bus_company_route'
            )
        ]

The default constraint error message is as following

Bus  Route with this  Shift already exists.

Is there any way out I can customize this constraint message to something like,

Bus Route and shift already in use please validate again

Answer 1

I just figured out how to create a custom UniqueConstraint error while using the CBV CreateView and the form ModelForm.

On the ModelForm I added this:

def validate_unique(self):
    """
    Call the instance's validate_unique() method and update the form's
    validation errors if any were raised.
    """
    exclude = self._get_validation_exclusions()
    try:
        self.instance.validate_unique(exclude=exclude)
    except ValidationError as e:
        error = {'__all__': "Custom error message."}
        self._update_errors(error)

This is mostly the class's default code, except I edited the contents in the except block.

Answer 2

You could use a try and except statement to catch the UniqueConstraint error, and raise your own instead. As far as I know, django doesn't have any provisions to override the unique constraint error directly, so this may be considered as best practice.

Implementation of the idea:

bus_route = BusRoute(**field_data)
try:
    bus_route.save()
except IntegrityError as err:
    raise CustomException('CUSTOM ERROR MESSAGE')