Question

The problem

Add custom validation to a form field in Django 1.3, the form is created by the generic view CreateView.

The model

class Picture(models.Model):
    file = models.ImageField(upload_to=get_image_path)
    filename = models.CharField(max_length=50, blank=True)
    user = models.ForeignKey(User, editable=False)
    upload_date = models.DateTimeField(auto_now_add=True,editable=False)

Generic view CreateView, a bit modified

class PictureCreateView(CreateView):
    model = Picture

    def clean_file(self,form):
        if image:
            if image._size > settings.MAX_IMAGE_SIZE:
                raise ValidationError("Image file too large ( > 20mb )")
        else:
             raise ValidationError("Couldn't read uploaded image")

    def get_form(self, form_class):
        form = super(PictureCreateView, self).get_form(form_class)
        form.instance.user = self.request.user
        return form

    def form_invalid(self, form):
        ...omitted none important code...
        response = JSONResponse(data, {}, response_mimetype(self.request))
        response['Content-Disposition'] = 'inline; filename=files.json'
        return response

    # Called when we're sure all fields in the form are valid
    def form_valid(self, form):
        ...omitted none important code...
        response = JSONResponse(data, {}, response_mimetype(self.request))
        response['Content-Disposition'] = 'inline; filename=files.json'
        return response

My question is: How can I do custom validation on the file field, before form_valid() is reached?

In short, what I’ve done so far

According to the documentation here – https://docs.djangoproject.com/en/dev/ref/forms/validation/
I should be able to override the file fields form validator, which I’m trying to do with clean_file()
“The clean_() method in a form subclass – where is replaced with the name of the form field attribute. ”
This would have been easy if I had created the form manually, but it’s created by Django from the model by the generic view.

My current solution, which is a ugly hack:
You can see that I’ve overridden form_valid() and form_invalid(), in form_valid() I now call clean_file()
and if it’s a error I call form_invalid(). This creates a few problems, for example I need to create the error message response manually.

Answer 1

Why not create your modelform ?

from django import forms

class PictureForm(forms.ModelForm):
    def clean_file(self,form):
        if image:
            if image._size > settings.MAX_IMAGE_SIZE:
                raise ValidationError("Image file too large ( > 20mb )")
        else:
            raise ValidationError("Couldn't read uploaded image")

    class Meta:
        model = Picture

Then you could use it in your view with the form_class attribute:

class PictureCreateView(CreateView):
    form_class = PictureForm

    # .... snip