Inject errors into already validated form?

Question

After my form.Form validates the user input values I pass them to a separate (external) process for further processing. This external process can potentially find further errors in the values.

Is there a way to inject these errors into the already validated form so they can be displayed via the usual form error display methods (or are there better alternative approaches)?

One suggestions was to include the external processing in the form validation, which is not ideal because the external process does a lot more than merely validate.

Answer 1

Form._errors can be treated like a standard dictionary. It's considered good form to use the ErrorList class, and to append errors to the existing list:

from django.forms.utils import ErrorList
errors = form._errors.setdefault("myfield", ErrorList())
errors.append(u"My error here")

And if you want to add non-field errors, use django.forms.forms.NON_FIELD_ERRORS (defaults to "__all__") instead of "myfield".

Answer 2

For Django 1.7+, you should use form.add_error() instead of accessing form._errors directly.

Documentation: https://docs.djangoproject.com/en/stable/ref/forms/api/#django.forms.Form.add_error

Answer 3

You can add additional error details to the form's _errors attribute directly:

https://docs.djangoproject.com/en/1.5/ref/forms/validation/#described-later https://docs.djangoproject.com/en/1.6/ref/forms/validation/#modifying-field-errors