How to clone a model instance without cloning database relationship?

Question

I'm building a cart model with the following code.

from django.db import models

class Item(models.Model):
    name = models.CharField(max_length=200)
    price = models.DecimalField(max_digits=8, decimal_places=2)

    def __str__(self):
        return self.name

class Order(models.Model):
    date = models.DateTimeField(auto_now_add=True)
    transcation_id = models.CharField(max_length=200, null=True)

    def __str__(self):
        return str(self.date)

class OrderItem(models.Model):
    item = models.ForeignKey(Item, on_delete=models.CASCADE, blank=True, null=True)
    order = models.ForeignKey(Order, on_delete=models.CASCADE, blank=True, null=True)
    quantity = models.IntegerField(default=0, blank=True, null=True)

The many-to-one relationship between Item and Order allows one Order to contain many Item and that looks fine.

A model instance can be simply cloned as already answer in this question.

My problem is, if the price of an Item is changed. The price of contained items in Order is change too. But I don't want it to be changed. In the situation that customer already make a purchase, the price cannot be change. Is there anyway to clone the Order instance that completely not related to the other model?

Aayush Agrawal · Accepted Answer · 2020-07-14T11:12:38.817

0

Save the price manually

class OrderItem(models.Model):
    item = models.ForeignKey(Item, on_delete=models.CASCADE, blank=True, null=True)
    order = models.ForeignKey(Order, on_delete=models.CASCADE, blank=True, null=True)
    quantity = models.IntegerField(default=0, blank=True, null=True)
    price = price = models.DecimalField(max_digits=8, decimal_places=2, null=True, default=None)
    def save():
        if self.pk == None:
            self.price = self.item.price
            super(OrderItem, self).save()

edited Jul 14 '20 at 11:12

answered Jul 14 '20 at 10:27

Aayush Agrawal

1,354
1
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It's error. Exception Value: save() takes 0 positional arguments but 1 was given. – Jul 14 '20 at 10:44
add a self there def save(self): – Aayush Agrawal Jul 14 '20 at 10:46
Exception Value: name 'item' is not defined – Jul 14 '20 at 11:05
self.price = self.item.price – Aayush Agrawal Jul 14 '20 at 11:05
Thank you so much. There is a bit editing needed. `super(OrderItem, self).save()` – Jul 14 '20 at 11:12

How to clone a model instance without cloning database relationship?

1 Answers1