accounts/models.py

class Role(models.Model):

    ROLE_CHOICES = (
        ('agent', 'Agent'),
        ('agency', 'Agency'),
        ('manufacturer', 'Manufacturer'),
    )
    role = models.CharField(max_length=15, choices=ROLE_CHOICES)

    def __str__(self):
        return self.role


class User(AbstractUser):

    role = models.ForeignKey(
        Role,
        on_delete=models.CASCADE,
        blank=True,
        null=True,
    )

    def __str__(self):
        return self.username

    def save(self, *args, **kwargs):
        if not self.pk:  # the instance is created
            self.role, created = Role.objects.get_or_create(role="agent")
        return super().save(*args, **kwargs)




agency/models.py

class Agency(models.Model):

    owner = models.OneToOneField(User, on_delete=models.CASCADE)
    name = models.CharField(
        max_length=200,
        blank=False,
        null=False)
    city = models.CharField(max_length=150, blank=False, null=False)
    street = models.CharField(max_length=150, blank=True, null=True)
    country = models.CharField(max_length=150, blank=True, null=True)
    mobile_number = PhoneNumberField()
    email = models.EmailField(blank=False, null=False)
    vat_number = models.CharField(max_length=40, blank=False, null=False)

agents/models.py

class Agent(models.Model):

    SEX_CHOICE = (
        ('male', 'Male'),
        ('female', 'Female'),
    )
    owner = models.OneToOneField(User, on_delete=models.CASCADE)
    agencies = models.ForeignKey(
        Agency,
        related_name="agents",
        on_delete=models.CASCADE)
    manufacturers = models.ForeignKey(
        Manufacturer,
        related_name="agents_manufacturer",
        on_delete=models.CASCADE,
        blank=True,
        null=True)
    date_of_birth = models.DateField(blank=True, null=True)
    sex = models.CharField(max_length=6, choices=SEX_CHOICE)
    city = models.CharField(max_length=150, blank=False, null=False)
    street = models.CharField(max_length=150, blank=True, null=True)
    country = models.CharField(max_length=150, blank=True, null=True)
    mobile_number = PhoneNumberField()



class Manufacturer(models.Model):

    owner = models.OneToOneField(
        User, on_delete=models.CASCADE, related_name="manufacturer")
    agency = models.ForeignKey(
        Agency,
        blank=True,
        null=True,
        related_name="agency_manufacturer",
        on_delete=models.CASCADE)
    name = models.CharField(
        max_length=200,
        blank=False,
        null=False)
    city = models.CharField(max_length=150, blank=False, null=False)
    street = models.CharField(max_length=150, blank=True, null=True)
    country = models.CharField(max_length=150, blank=True, null=True)



shops/models.py

class Shop(models.Model):

    agent = models.ForeignKey(Agent, on_delete=models.CASCADE, null=True)
    name = models.CharField(max_length=150, blank=False, null=False)
    city = models.CharField(max_length=150, blank=False, null=False)
    street = models.CharField(max_length=150, blank=True, null=True)
    country = models.CharField(max_length=150, blank=True, null=True)
    mobile_number = PhoneNumberField()
    vat_number = models.CharField(max_length=40, blank=False, null=False)

    def __str__(self):
        return self.name


class Category(models.Model):

    name = models.CharField(max_length=150, db_index=True)
    slug = models.SlugField(max_length=150, db_index=True)
    description = models.TextField()
    parent = models.ForeignKey('self', on_delete=models.CASCADE, null=True, blank=True)

    def __str__(self):
        return self.name


class Product(models.Model):

    product_code = models.CharField(max_length=50, blank=False, null=False)
    agencies = models.ForeignKey(
        Agency,
        on_delete=models.CASCADE,
        related_name="product_agencies",
        null=True)
    manufacturer = models.ForeignKey(
        Manufacturer,
        related_name="product_manufacturers",
        on_delete=models.CASCADE,
        null=True)
    name = models.CharField(max_length=120, db_index=True)
    category = models.ForeignKey(
        Category,
        related_name="product_category",
        null=True,
        on_delete=models.CASCADE)
    price = models.DecimalField(max_digits=10, decimal_places=2)
    min_price = models.DecimalField(max_digits=10, decimal_places=2)
    packaging = models.CharField(max_length=120)
    package_dimension = models.CharField(max_length=120, blank=True, null=True)
    package_weight = models.PositiveIntegerField(default=1)


orders/models.py

class Order(models.Model):

    product_code = models.CharField(max_length=50, blank=False, null=False)
    agents = models.ForeignKey(
        Agent,
        on_delete=models.CASCADE,
        related_name="order_agents")
    shops = models.ForeignKey(
        Shop,
        related_name="order_manufacturers",
        on_delete=models.CASCADE)
    product = models.ForeignKey(
        Product,
        related_name="order_product",
        on_delete=models.CASCADE)
    quantity = models.PositiveIntegerField(default=1)
    unit = models.CharField(max_length=50)