I have an ecommerce store app that have those apps:

1. core: specific for the ecommerce store app needs.
2. likes: independent reusable app that is supposed to be used with different models from other apps.
3. store: independent reusable app that has the models and views for the ecommerce app.

Now I want to add the ability for the user to like a product, so I want to add a like (from likes) to the product (from store), how can I do it without adding explicit dependency (import likes in store) between the two apps?

The LikedItem model from likes app:

from django.conf import settings
from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes.fields import GenericForeignKey

class LikedItem(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey()

The Product model from the store app:

class Product(models.Model):
    title = models.CharField(max_length=255)
    slug = models.SlugField()
    description = models.TextField(null=True, blank=True)
    unit_price = models.DecimalField(
        max_digits=6,
        decimal_places=2,
        validators=[MinValueValidator(1)])
    inventory = models.IntegerField(validators=[MinValueValidator(0)])
    last_update = models.DateTimeField(auto_now=True)
    collection = models.ForeignKey(
        Collection, on_delete=models.PROTECT, related_name='products')
    promotions = models.ManyToManyField(Promotion, blank=True)

    def __str__(self) -> str:
        return self.title

    class Meta:
        ordering = ['title']

I tried implementing this in the core app, I started with creating a CustomProduct model that extends the Product model and adds likes = GenericRelation(LikedItem), but things became messy in the serializer part, as I couldn’t extend the Product serializer and add the likes field to it, and I felt that I may need to completly implement the Product model only in the core app.