title: Why save() method need to self argument in django?
body: <p>I am trying to solve this problem for over 3 days but can't solve it yet. I know self use for a method that is under a class, but I am working with method base view so why this error occurs when I try to save the OrderItem model?</p>
  <p>models.py</p>
  <pre><code>class OrderItem(BaseModel):
      user = models.ForeignKey(User, on_delete=models.CASCADE)
      customer = models.ForeignKey(Customer, on_delete=models.CASCADE)
      cart = models.ManyToManyField(Cart, blank=True)
      name = models.CharField(max_length=200)
      district = models.ForeignKey(District, on_delete=models.CASCADE)
      city = models.CharField(max_length=200)
      postal_code = models.SmallIntegerField()
      area = models.TextField()
      phone = models.CharField(max_length=12)
      status = models.CharField(max_length=20, choices=STATUS_CHOICE, default=&quot;accepted&quot;,blank=True, null=True)
      email = models.EmailField()
  
      def __str__(self):
          return self.user.email
  
  </code></pre>
  <p>views.py</p>
  <pre><code>
  def checkout(request):
      context={}
      subtotal =0
      forms = OrderItemForm()
      context['forms'] = forms
      if request.user.is_authenticated:
          user = request.user
          cart = Cart.objects.filter(user=user).order_by('-id')
          for product in cart:
              subtotal += product.total_cost
          context['subtotal'] = subtotal
          customer = Customer.objects.get(user=user)
          if request.POST:
              form = OrderItemForm(request.POST)
              if form.is_valid():
                  instance = OrderItemForm.save(commit=False)
                  instance.user = user
                  instance.customer = customer
                  instance.cart = cart
                  instance.save()
              else:
                  messages.warning(request, form.errors)
      return render(request, 'checkout.html', context)
  </code></pre>
  <p>command-line error:</p>
  <pre><code>    response = wrapped_callback(request, *callback_args, **callback_kwargs)
    File &quot;C:\bitspirits\rndm\shop\views.py&quot;, line 76, in checkout
      instance = OrderItemForm.save(commit=False)
  TypeError: save() missing 1 required positional argument: 'self'
  </code></pre>