How to Automatically Copy Product Attributes to Variants in Django Models?

I am building an e-commerce website in Django where:

A Product can have multiple variants.
Each product has attributes (e.g., color, storage, display size).
I want each variant to automatically inherit all attributes from the main product when it is created.

Models (`models.py`)

from django.db import models

class Product(models.Model):
    name = models.CharField(max_length=255)

class ProductVariant(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE, related_name="variants")
    name = models.CharField(max_length=255)  # Example: "Iphone 16 Black 128GB"

class ProductAttribute(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE, related_name="attributes")
    attribute_name = models.CharField(max_length=255)
    attribute_value = models.TextField()

What I Want to Achieve:

When a ProductVariant is created, it should automatically copy all attributes from its main product.
What is the best way to do this in Django?

I want a clean and efficient solution that works well even if I have many variants.
Any guidance would be appreciated. Thank you!

To achieve this in Django, you can use Django signals to automatically copy the attributes from the main product to the variant when a ProductVariant is created. Here's how you can do it:

Define your models as you have done.
Create a signal that listens for the post_save event on the ProductVariant model.
Copy the attributes from the main product to the variant when the signal is triggered.

Here's how you can implement this:

# models.py
from django.db import models
from django.db.models.signals import post_save
from django.dispatch import receiver

class Product(models.Model):
    name = models.CharField(max_length=255)

class ProductVariant(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE, related_name="variants")
    name = models.CharField(max_length=255)  # Example: "Iphone 16 Black 128GB"

class ProductAttribute(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE, related_name="attributes")
    attribute_name = models.CharField(max_length=255)
    attribute_value = models.TextField()

class ProductVariantAttribute(models.Model):
    variant = models.ForeignKey(ProductVariant, on_delete=models.CASCADE, related_name="variant_attributes")
    attribute_name = models.CharField(max_length=255)
    attribute_value = models.TextField()

# signals.py
from django.db.models.signals import post_save
from django.dispatch import receiver
from .models import ProductVariant, ProductAttribute, ProductVariantAttribute

@receiver(post_save, sender=ProductVariant)
def copy_product_attributes(sender, instance, created, **kwargs):
    if created:
        product_attributes = ProductAttribute.objects.filter(product=instance.product)
        for attr in product_attributes:
            ProductVariantAttribute.objects.create(
                variant=instance,
                attribute_name=attr.attribute_name,
                attribute_value=attr.attribute_value
            )

# apps.py
from django.apps import AppConfig

class YourAppConfig(AppConfig):
    name = '<your_app_name>'

    def ready(self):
        import your_app_name.signals

In this implementation:

Models: Added a ProductVariantAttribute model to store attributes for each variant.
Signals: Created a signals.py file where the post_save signal for ProductVariant is defined. This signal copies the attributes from the main product to the variant when a new variant is created.
AppConfig: Updated the AppConfig to ensure the signals are imported and ready when the app starts.

Make sure to replace 'your_app_name' with the actual name of your Django app.

This approach ensures that whenever a new ProductVariant is created, it automatically inherits all attributes from the main product, keeping your code clean and efficient

"I want each variant to automatically inherit all attributes from the main product when it is created."

Then you should use INHERITANCE, a core OOP feature, that does exactly that. A child model inherits all methods and attributes from the parent model.

Look here: Django inheritance

from django.db import models


class Parent(models.Model):
    name = models.CharField(max_length=100)
    age = models.PositiveIntegerField()

    class Meta:
        abstract = True


class Child(Parent):
    location = models.CharField(max_length=5)

The Child model will have both the name and age attribute of Parent and in addition the location attribute, because it inherits from Parent .