如何在Django模型的外键中更改值？

Question

Cart_Items , Cart , Order models .i want for my shopping website , that after a ordering a product , a value increased , but i cant access it .

i tried to get it by pr=Products.objects.all() ci=Cart_Items.filter(product_id=pr)

my models.py:

order model:

   class Order(models.Model):
    user = models.ForeignKey(User,blank=True,null=True,on_delete=models.CASCADE)
    order_id  = models.CharField(  max_length=120,default="ABC",unique=True)
    cart  =   models.ForeignKey(Cart,on_delete=models.CASCADE)
    statu = models.CharField(max_length=120,choices=STATUS_CHOICES,default="Started")

product model:

    class Products(models.Model):
     title           =   models.CharField(max_length=250)
     order_qty       =   models.IntegerField(default=0)

Cart_Items model:

     class Cart_Items(models.Model):
          cart      =  models.ForeignKey('Cart',null=True,blank=True,on_delete=models.CASCADE)
         product_id = models.ForeignKey(Products,null=True,blank=True,on_delete=models.CASCADE)

cart model :

class Cart(models.Model):
    total      = models.IntegerField(default=0)
    timestamp  = models.DateTimeField(auto_now_add=True,auto_now=False)
    date       = models.DateTimeField(auto_now_add=False,auto_now=True)
    isPaid     = models.BooleanField(default=False)

my views.py:

    def add(request):
        cart_items=Cart_Items.objects.all()
         for item in cart_items:
            print(item.product_id.order_qty)
            item.product_id.order_qty +=1
         render(request,"home.html",{})

i want after ordering a product , order_qty , increased , how can i do that ? i must do it by Cart_items ? or there is another ways ? plz help.

Answer 1

You have to call save method, after you change a value:

 def add(request):
    cart_items=Cart_Items.objects.all()
     for item in cart_items:
        print(item.product_id.order_qty)
        item.product_id.order_qty +=1
        item.save()
     render(request,"home.html",{})

Or like @Wilem said, you can count the quantity by the number of all the items in the order:

   Order.objects.all().count