Django Admin: How to only save inline model not parent

Question

I have following simplified setup:

• A model based on legacy data which can't be changed. Therefore I raise a ValidationError to make the user aware that there was no change made. The form fields are readonly and I could use a simple 'pass' but I prefer to get the message that save() didn't do what it was intended to do instead of just do silently nothing.
• Now I'm extending the legacy data with a 2nd model which should be editable. It is included it into the legacy model's ModelAdmin as inline. I could include the CommentModel itself as a ModelAdmin, but as the LegacyModel inherits lots of functionality from parent-classes this gets complicated and un-dry.

What I want is to perform the "save" operation only on the inline-model. I thought as all fields are readonly it should work fine. Can someone give me a hint to do this in clean way?

class Legacy(models.Model):

    legacyData = models.TextField()

    def clean(self):
        raise ValidationError("%s model is readonly." % self._meta.verbose_name.capitalize())

class Comment(models.Model):

    legacy = models.OneToOneField(Legacy)
    comment = models.TextField()


class LegacyAdmin(admin.ModelAdmin):

    def __init__(self, *args, **kwargs):
        self.readonly_fields = self.fields
        super(LegacyAdmin, self).__init__(*args, **kwargs)

    model = Legacy
    inlines = (CommentInline, )

Thanks a lot for your time! :)

Answer 1

Rather than raising an exception in clean(), you could override the legacy's save() and use http://docs.djangoproject.com/en/dev/ref/contrib/messages/ to tell your user what didn't happen.