Django Field Notes

Model_and_Form_Validations.md

Model + Form validations

Some of Django's choices on how to handle data integrity are wrong, or at the very least, unexpected to the uninitiated developers. I'm not here to pass judgement; like many people, I'd just like to get back to doing real work. Some notes on how to stay safe in Django:

What should I know?

• Django now has both Form validations and Model validations
• Django used to only have Form validations
• Form’s is_valid() performs model validation automatically
• full_clean() is never actually called by Django (see ticket #13100)

What should I do?

• Stay DRY
• Read http://schneck.cc/node/41
• Put model validation only in clean() to avoid confusion
• Never overwrite full_clean()
• Use model validation whenever possible.
• Before you save an object, apply full_clean() on it.

I'm paranoid; can Django help?

Always run model validation before saving a model instance

# http://djangosnippets.org/snippets/2319/
from django.db.models.signals import pre_save

def validate_model(sender, **kwargs):
    if 'raw' in kwargs and not kwargs['raw']:
        kwargs['instance'].full_clean()

pre_save.connect(validate_model, dispatch_uid='validate_models')

Examples

Add field-specific errors in form.clean()

# http://djangosnippets.org/snippets/337/

from django.forms.utils import ErrorList

def clean(self):
    cleaned = self.cleaned_data
    errors = False

    #
    # Validate stuff here!
    #

    if there_are_errors_for_field1:
        self._errors['field1'] = self._errors.get('field1', ErrorList())
        self._errors['field1'].append(_("Field 1 is invalid"))
        errors = True
    if there_are_errors_for_field2:
        self._errors['field2'] = self._errors.get('field2', ErrorList())
        self._errors['field2'].append(_("Field 2 is invalid"))
        errors = True

    non_field_errors = []
    if there_are_other_errors:
        non_field_errors.append(_("Non field error"))
        errors = True

    if errors:
        raise form.ValidationError(non_field_errors)
    return cleaned

Validate unique_together with one field excluded from form

# http://stackoverflow.com/questions/6892162/django-1-3-createview-modelform-unique-together-validation-with-one-field-exclud

class SubscriberForm(ModelForm):
    class Meta:
        model = Subscriber
        exclude = ('user')

class SubscriberCreateView(AuthCreateView):
    model = Subscriber
    form_class = SubscriberForm
    template_name = "forms/app.html"
    success_url = "/app/subscribers/"

    def form_valid(self, form):
        self.object = form.save(commit=False)
        self.object.user = self.request.user
        try:
            self.object.full_clean()
        except ValidationError:
            from django.forms.util import ErrorList
            form._errors["email"] = ErrorList([u"You already have an email with that name."])
            return super(SubscriberCreateView, self).form_invalid(form)

        return super(SubscriberCreateView, self).form_valid(form) 

Access request.user from any ModelForm, including Admin

# http://stackoverflow.com/questions/1057252/django-how-do-i-access-the-request-object-or-any-other-variable-in-a-forms-clea

class MyModelAdmin(admin.ModelAdmin):
    form = MyCustomForm
    def get_form(self, request, obj=None, **kwargs):
        ModelForm = super(MyModelAdmin, self).get_form(request, obj, **kwargs)
        def form_wrapper(*args, **kwargs):
            return ModelForm(request=request, *args, **kwargs)
        return form_wrapper

class MyCustomForm(forms.ModelForm):
    def __init__(self, request=None, *args, **kwargs):
        self.request = request
        super(MyCustomForm, self).__init__(*args, **kwargs)

You can then access the request object from any method of ModelForm with self.request.