How to implement method from Model to form - django

Question

I have in my models.py method of Model:
class Book(model.models):
...
def generate_tag(self):
return f'{self.inspection.series_of_tags}-{str(self.tag_number).zfill(7)}'
I want to implement this method in my form when I push on update view it generate new tag:
class TagForm(core.ModelForm):
def save(self, commit=True):
instance = super().save(commit=False)
if self.cleaned_data['tag_number']:
instance = Book.generate_tag(self.instance)
if commit:
instance.save()
return instance
class Meta:
model = Book
fields = (
'tag_number',
)
my views.py
class BookUpdateView(BookViewMixin, core.UpdateView):
form_class = TagForm
template_name = 'book.html'
I want that when I click update view - my field 'tag number' will give method from model 'generate_tag' when I save my Form!What I am doing wrong in my code?

Answer 1

So what you're doing in your form at the moment would work for a class method, Book.generate_tag(self.instance). That's calling a method on the Book class.
Your save() also won't work correctly because it may return a string, not a Book object;
def save(self, commit=True):
instance = super().save(commit=False)
if self.cleaned_data['tag_number']:
instance = Book.generate_tag(self.instance)
# Here instance is a string, because `generate_tag(self.instance)` returns a string.
if commit:
instance.save()
return instance
You probably want to exclude the field from the form as it doesn't get a value initially. Then you can generate the value in the view.
class TagForm(core.ModelForm):
class Meta:
model = Book
exclude = (
'tag_number',
)
class BookUpdateView(BookViewMixin, core.UpdateView):
form_class = TagForm
template_name = 'book.html'
def form_valid(self, form):
"""If the form is valid, save the associated model and generate the tag."""
self.object = form.save(commit=False)
tag = self.object.generate_tag()
# do something with your generated tag, like assign it to a field.
self.object.save()
return super().form_valid(form)