Question

I’ve got a model with a unique_together constraint.

class Postit(models.Model):
    """Represents a single post-it."""
    x_axis = models.PositiveIntegerField(_('X axis'))
    y_axis = models.PositiveIntegerField(_('Y axis'))
    content = models.CharField(_('Content'), max_length=140, default='')

    class Meta:
        unique_together = ('x_axis', 'y_axis')

If I use a form to create a new post-it, the constraint is checked, and in case of a conflict, the error is listed in the non_field_errors property. Fine.

My problem is that I want to launch a different action depending of the kind of form error. I want a specific action if there is a unique constraint error, and another action for any other kind of errors.

Given that my app will be translated in several languages, how do I know if the form is invalid because of the constraint or for another reason?

Answer 1

Bear in mind that you can translate the string you’re comparing if you want to just check non_field_errors.

from django.utils.translation import ugettext_lazy as _
if _('Some error text') in self._errors['__all__']:
    # do something

That’s not really the most elegant solution though. Your best bet is to simply verify the unique_together constraint yourself in Model.clean or Model.validate_unique and respond accordingly.