example

class Category(models.Model):
    name = models.CharField(max_length=100)


class Product(models.Model):
    name = models.CharField(max_length=100)
    description = models.TextField(null=True, blank=True)
    price = models.DecimalField(max_digits=10, decimal_places=2)
    category = models.ForeignKey("Category", on_delete=models.CASCADE) # ONE TO MANY ВРЪЗКА С Category
    is_available = models.BooleanField(default=True)

    def __str__(self):

        return f"{self.category.name}: {self.name}"

class Customer(models.Model):
    username = models.CharField(max_length=50, unique=True)


class Order(models.Model):
    customer = models.ForeignKey("Customer", on_delete=models.CASCADE) # ONE TO MANY ВРЪЗАКА С Customer
    products = models.ManyToManyField("Product", through="OrderProduct") # MANY TO MANY ВРЪЗКА С Product


class OrderProduct(models.Model):
    order = models.ForeignKey("Order", on_delete=models.CASCADE) # ONE TO MANY ВРЪЗКА С Order
    product = models.ForeignKey("Product", on_delete=models.CASCADE) # ONE TO MANY ВРЪЗКА С Product
    quantity = models.PositiveIntegerField()