[1.8.x] Fixed #24988 -- Documented passing a dictionary of ValidationErrors to ValidationError

    import datetime

    from django.core.exceptions import ValidationError

    from django.db import models

    from django.utils.translation import ugettext_lazy as _

    class Article(models.Model):

        ...

        def clean(self):

            # Don't allow draft entries to have a pub_date.

            if self.status == 'draft' and self.pub_date is not None:

                raise ValidationError('Draft entries may not have a publication date.')

                raise ValidationError(_('Draft entries may not have a publication date.'))

            # Set the pub_date for published items if it hasn't been set already.

            if self.status == 'published' and self.pub_date is None:

                self.pub_date = datetime.date.today()

        def clean(self):

            # Don't allow draft entries to have a pub_date.

            if self.status == 'draft' and self.pub_date is not None:

                raise ValidationError({'pub_date': 'Draft entries may not have a publication date.'})

                raise ValidationError({'pub_date': _('Draft entries may not have a publication date.')})

            ...

If you detect errors in multiple fields during ``Model.clean()``, you can also

pass a dictionary mapping field names to errors::

    raise ValidationError({

        'title': ValidationError(_('Missing title.'), code='required'),

        'pub_date': ValidationError(_('Invalid date.'), code='invalid'),

    })

Finally, ``full_clean()`` will check any unique constraints on your model.

.. method:: Model.validate_unique(exclude=None)