Question

This may be a dumb question, but I’m a bit unsure if it’s safe to manually set the cleaned_data. The docs says:

Once is_valid() returns True, you can process the form submission
safe in the knowledge that it conforms to the validation rules defined
by your form. While you could access request.POST directly at this
point, it is better to access form.cleaned_data. This data has not
only been validated but will also be converted in to the relevant
Python types for you.

For more context, say we have a modelform which has several fields such as a book’s title, book’s author, and a field which asks for a url.

The form conditions are: if the url field is empty, the user must provide the title and author. If the url field is given and nothing else, I would parse the html from the given url and extract the title and author automatically for the user.

In the case where I automatically grab the title and author from the url, what would be the best way to handle saving this data to the model, since the form would return an empty cleaned_data for author and title? I made sure the data parsed will conform to the validate rules I have in the model, but setting cleaned_data like this seems suspicious.

In modelform class:

def save(self, commit = True, *args, **kwargs):
    parsed_title = ... # String returned by my html parsing function
    parsed_author = ... # String returned by my html parsing function
    self.cleaned_data['title'] = parsed_title
    self.cleaned_data['author'] = parsed_author

EDIT:

Thanks, I made it like so:

def save(self, commit=True, *args, **kwargs):
     instance = super(BookInfoForm, self).save(commit=commit, *args, **kwargs)
     ....
     instance.title = parsed_title
     instance.author = parsed_author

     return instance

This is a bit off topic since you’ve already answered the original question, but the above code breaks some other part. Instead of saving the compiled info to http://..../media/books/<id> where <id> is the book id, it saves it to http://..../media/books/None.

I have a add/edit function in my views.py that handles adding and editing:

def insert_or_modify(request, id=None):
    if id is not None:
         book = BookModel.objects.get(pk=id)
    else:
         book = BookModel()

   if request.method == 'POST':
       form = BookInfoForm(request.POST, instance=book)
       if form.is_valid():
           form.save()

   ....
   
   return render_to_response(...)

Is there a way to make sure the id is present so that I won’t get id=None? I guess more specifically, in the save() in the modelform, is there a way to create a new instance with an id if instance.id = None? Although I thought calling super(ModelForm, self).save(…) would do that for me?

Thanks again!

Answer 1

In the case you present, your intention isn’t setting the cleaned_data, but the model data. Therefore, instead of setting cleaned_data in the save method, just set the attributes of self.instance and then save it.

About setting cleaned_data manually, I don’t think it’s necessarily wrong, it may make sense to do it in the form’s clean method for some cross-field validation, although it’s not a common case.