adding errors to Django form errors.__all__ - django

Question

How do I add errors to the top of a form after I cleaned the data? I have an object that needs to make a REST call to an external app (google maps) as a pre-save condition, and this can fail, which means I need my users to correct the data in the form. So I clean the data and then try to save and add to the form errors if the save doesn't work:
if request.method == "POST":
#clean form data
try:
profile.save()
return HttpResponseRedirect(reverse("some_page", args=[some.args]))
except ValueError:
our_form.errors.__all__ = [u"error message goes here"]
return render_to_response(template_name, {"ourform": our_form,},
context_instance=RequestContext(request))
This failed to return the error text in my unit-tests (which were looking for it in {{form.non_field_errors}}), and then when I run it through the debugger, the errors had not been added to the forms error dict when they reach the render_to_response line, nor anywhere else in the our_form tree. Why didn't this work? How am I supposed to add errors to the top of a form after it's been cleaned?

Answer 1

You really want to do this during form validation and raise a ValidationError from there... but if you're set on doing it this way you'll want to access _errors to add new messages. Try something like this:
from django.forms.util import ErrorList
our_form._errors["field_name"] = ErrorList([u"error message goes here"])

Answer 2

Non field errors can be added using the constant NON_FIELD_ERRORS dictionary key (which is __all__ by default):
from django import forms
errors = my_form._errors.setdefault(forms.forms.NON_FIELD_ERRORS, forms.util.ErrorList())
errors.append("My error here")

Answer 3

In Django 1.7 or higher, I would do:
form.add_error(field_name, "Some message")
The method add_error was added in 1.7. The form variable is the form I want to manipulate and field_name is the specific field name or None if I want an error that is not associated with a specific field.
In Django 1.6 I would do something like:
from django.forms.forms import NON_FIELD_ERRORS
errors = form._errors.setdefault(field_name, form.error_class())
errors.append("Some message")
In the code above form is the form I want to manipulate and field_name is the field name for which I want to add an error. field_name can be set to NON_FIELD_ERRORS to add an error not associated with a specific field. I use form.error_class() to generate the empty list of error messages. This is how Django 1.6 internally creates an empty list rather than instantiate ErrorList() directly.

Answer 4

You should raise the validationerror.
Why not put the verification within the form's clean method
class ProfileForm(forms.Form):
def clean(self):
try:
#Make a call to the API and verify it works well
except:
raise forms.ValidationError('Your address is not locatable by Google Maps')
that way, you just need the standard form.is_valid() in the view.

Answer 5

You're almost there with your original solution. Here is a base Form class I built which allows me to do the same thing, i.e. add non-field error messages to the form:
from django import forms
from django.forms.util import ErrorDict
from django.forms.forms import NON_FIELD_ERRORS
class MyBaseForm(forms.Form):
def add_form_error(self, message):
if not self._errors:
self._errors = ErrorDict()
if not NON_FIELD_ERRORS in self._errors:
self._errors[NON_FIELD_ERRORS] = self.error_class()
self._errors[NON_FIELD_ERRORS].append(message)
class MyForm(MyBaseForm):
....
All my forms extend this class and so I can simply call the add_form_error() method to add another error message.

Answer 6

I'm not sure how horrible of a hack this is (I've only really worked on two Django projects up until this point) but if you do something like follows you get a separate error message that is not associated with a specific field in the model:
form = NewPostForm()
if something_went_horribly_wrong():
form.errors[''] = "You broke it!"

Answer 7

If the validation pertains to the data layer, then you should indeed not use form validation. Since Django 1.2 though, there exists a similar concept for Django models and this is certainly what you shoud use. See the documentation for model validation.