Django generic create view . Can we add conditions to save data from the form?
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This is what my code looks like and I want to add some condition to the Borrower create view like if the stock method of book returns 0 then don’t list that book in field while creating a new borrower or if it isn’t possible at least throw some error while adding borrower to that book.
models.py:
class Book(models.Model):
id = models.UUIDField(primary_key=True, unique=True,
default=uuid.uuid4, editable=False)
title = models.CharField(max_length=200)
author = models.CharField(max_length=100)
summary = models.TextField(
max_length=1000, help_text="Enter a brief description of the book")
isbn = models.CharField('ISBN', max_length=13,
help_text='13 Character https://www.isbn-international.org/content/what-isbn')
genre = models.ManyToManyField(
Genre, help_text="Select a genre for this book")
language = models.ForeignKey(
'Language', on_delete=models.SET_NULL, null=True)
total_copies = models.IntegerField()
pic = models.ImageField(blank=True, null=True, upload_to='books')
def stock(self):
total_copies = self.total_copies
available_copies = total_copies -
Borrower.objects.filter(book=self).count()
if available_copies > 0:
return available_copies
else:
return 0
def __str__(self):
return self.title
class Borrower(models.Model):
id = models.UUIDField(primary_key=True, unique=True,
default=uuid.uuid4, editable=False)
student = models.ForeignKey('Account', on_delete=models.CASCADE)
book = models.ForeignKey('Book', on_delete=models.CASCADE)
issue_date = models.DateField(
null=True, blank=True, help_text='YYYY-MM-DD', default=date.today)
return_date = models.DateField(
null=True, blank=True, help_text='YYYY-MM-DD')
def __str__(self):
return self.student.name.title()+" borrowed "+self.book.title.title()
def fine(self):
today = date.today()
fine = 0
if self.return_date <= today:
fine += 5 * (today - self.return_date).days
return fine
views.py:
class BorrowerView(LoginRequiredMixin, ListView):
model=Borrower
context_object_name='borrowers'
template_name = 'library/borrower_list.html'
def get_context_data(self, **kwargs):
context=super().get_context_data(**kwargs)
if self.request.user.is_admin or self.request.user.is_superuser:
context['borrowers']=context['borrowers']
else:
context['borrowers']=context['borrowers'].filter(student = self.request.user.id)
return context
class BorrowerCreate(LoginRequiredMixin, UserAccessMixin, CreateView):
model=Borrower
permission_required= 'borrowers.add_borrowers'
fields='__all__'
success_url=reverse_lazy('library:borrower-list')
def form_valid(self, form):
form.instance.user=self.request.user
return super(BorrowerCreate, self).form_valid(form)
class BorrowerDetail(LoginRequiredMixin, DetailView):
model=Borrower()
context_object_name='borrower'
template_name='library/borrower.html'
Answer
class Book(models.Model):
id = models.UUIDField(primary_key=True, unique=True,
default=uuid.uuid4, editable=False)
title = models.CharField(max_length=200)
author = models.CharField(max_length=100)
summary = models.TextField(
max_length=1000, help_text="Enter a brief description of the book")
isbn = models.CharField('ISBN', max_length=13,
help_text='13 Character https://www.isbn-international.org/content/what-isbn')
genre = models.ManyToManyField(
Genre, help_text="Select a genre for this book")
language = models.ForeignKey(
'Language', on_delete=models.SET_NULL, null=True)
total_copies = models.IntegerField()
pic = models.ImageField(blank=True, null=True, upload_to='books')
#new, use this to keep track of available books
available_copies = models.IntegerField()
def __str__(self):
return self.title
When any borrower borrows a copy of the book, you will subtract it from the total copies.
class BorrowerCreate(LoginRequiredMixin, UserAccessMixin, CreateView):
model=Borrower
permission_required= 'borrowers.add_borrowers'
fields='__all__'
success_url=reverse_lazy('library:borrower-list')
#remember to get the object using slug or 404
def form_valid(self, form):
instance = form.save(commit=False)
instance.user = self.request.user
book = Book.objects.get(id=instance.book.id)
#get the book id from the form and check if the book is still available, then subtract.
if book.available_copies > 0:
book.available_copies -= 1
book.save()
instance.save()
message.success(self.request, _("successful")
message.error(self.request, _("Book not in stock")
return super(BorrowerCreate, self).form_valid(form)
If user return the book and click returned. you can perform a similar action by adding to available copies.
This is not the solution, you can write a fat model with methods that takes care of both borrowing and return. Like this
def borrow(self):
self.available_copies -= 1
def returned(self):
self.available_copies += 1
You can call these two methods in different views or define a signal that call them using pre_save
Ist: Instead of defining a new method which you called stock, why not add stock as a field instead of making a database query.
2nd: calling the class inside the same class is not the best way to make queries inside the class.
3rd: To add a condition while adding an object, you need to override the save method of the object like this.
def save(self, *args, **kwargs):
# do_something() here.....
# then
return super().save(*args, **kwargs)
The above code will enable you to perform any action before saving the object.
Another way you can do this is inside the form_valid function like this.
def form_valid(self, form):
instance = form.save(commit=False)
# commit = False will make sure that the form is not saved
# then you can now query the database and check conditions like
if Borrower.object.all().count() > 0:
instance.save()
messages.success(self.request, _("saved successfully")
else:
messages.error(self.request, _("Error")
return redirect("URL")