Model.clean() [source]
This method should be used to provide custom model validation, and to modify attributes on your model if desired. For instance, you could use it to automatically provide a value for a field, or to do validation that requires access to more than a single field:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | import datetimefrom django.core.exceptions import ValidationErrorfrom django.db import modelsfrom 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.')) # 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() |
Note, however, that like Model.full_clean(), a model’s clean() method is not invoked when you call your model’s save() method.
In the above example, the ValidationError exception raised by Model.clean() was instantiated with a string, so it will be stored in a special error dictionary key, NON_FIELD_ERRORS. This key is used for errors that are tied to the entire model instead of to a specific field:
1 2 3 4 5 | from django.core.exceptions import ValidationError, NON_FIELD_ERRORStry: article.full_clean()except ValidationError as e: non_field_errors = e.message_dict[NON_FIELD_ERRORS] |
To assign exceptions to a specific field, instantiate the ValidationError with a dictionary, where the keys are the field names. We could update the previous example to assign the error to the pub_date field:
1 2 3 4 5 6 7 | 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({'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:
1 2 3 4 | 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.
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