Django overwriting data in mysql database

Hey I am creating a project in django where I keep track of orders. Now I want to add all the items to an orderline table to keep track of which items are ordered. But when I want to add multiple items from 1 order to the database it only enters the last one. My guess is that it overrides the previous one. This is my Orderline model class in django.

class OrderLine(models.Model):
product = models.ForeignKey(Product, on_delete=models.SET_NULL, null=True, blank=True)
order = models.ForeignKey(Order, on_delete=models.SET_NULL, null=True, blank=True)
quantity = models.IntegerField()
size = models.CharField(max_length=50)

def __str__(self):
    return self.to_dict()

def to_dict(self):
    return {
        'product': self.product.to_dict(),
        'order': self.order.to_dict(),
        'quantity': self.quantity,
        'size': self.size
    }

def add(self, product, order, quantity, size):
    self.product = Product.objects.get(id=product)
    self.order = Order.objects.get(id=order)
    self.quantity = quantity
    self.size = size
    self.save()
    return self.to_dict()

def add_orderline(self, product, order, quantity, size):
    if self.exists(product, order, size):
        orderline = OrderLine.objects.get(product=product, order=order, size=size)
        orderline.quantity += quantity
        orderline.save() 
        return orderline.to_dict()
    else:
        orderline = self.add(product, order, quantity, size)
        return orderline

def exists(self, product, order, size):
    return OrderLine.objects.filter(product=product, order=order, size=size).exists()

def get_all_by_order(self, order):
    return OrderLine.objects.filter(order=order)

This is the code that should create multiple orderlines.

for idx in range(len(cart_items)):
        orderline = order_line.add_orderline(cart_items[idx],uncomplete_order["id"], cart.get_by_user(body['user_id'])[idx]["quantity"], cart.get_by_user(body['user_id'])[idx]["size"])
        print(orderline)

NOTE: it is not important to know the data in the order_line.add_orderline() function i already checked the data and it is correct.

Now for my example I have 2 items in my cart_items but only the last one gets added. Im not sure if this is relevant information but I’m using a mysql database hosted on a lightsail server from AWS. if there is any more information you guys need, you can refer to it in the comments. All the help is greatly appreciated.

>Solution :

Your add method actually modifies an existing row and not create a new one. You probably want something like this:

@classmethod
def add(cls, product, order, quantity, size):
    obj = cls()
    obj.product = Product.objects.get(id=product)
    obj.order = Order.objects.get(id=order)
    obj.quantity = quantity
    obj.size = size
    obj.save()
    return obj.to_dict()

And then you should call it with OrderLine.add() to make it more clear you’re creating a new one and not doing something with an existing object.

You’re add_orderline is also being called on an existing object and self will point to that existing object. Maybe that should also be a @classmethod?