models.py

class OwnersDetails(models.Model):
    first_name = models.CharField(verbose_name="Фамилия", max_length=50, blank=True)
    last_name = models.CharField(verbose_name="Имя", max_length=50, blank=True)
    name_organization = models.CharField(verbose_name="Наименование организации", max_length=150, blank=True)
    inn_organization = models.BigIntegerField(verbose_name="ИНН организации", blank=True)
    person_number_phone = models.BigIntegerField(verbose_name="Номер телефона", blank=True)
    city = models.CharField(verbose_name="Город", max_length=100, blank=True)
    street = models.CharField(verbose_name="Улица", max_length=100, blank=True)
    house_number = models.CharField(verbose_name="Номер дома / офиса", max_length=50, blank=True)

    def __str__(self):
        return self.name_organization

    class Meta:
        verbose_name = "данные заказчика"
        verbose_name_plural = "данные заказчиков"
        indexes = [
            models.Index(fields=["inn_organization"]),
            models.Index(fields=["name_organization"])
        ]


class Device(models.Model):
    owners_details = models.ForeignKey(
        OwnersDetails,
        models.SET_NULL,
        related_name='owners_details_device',
        blank=True,
        null=True
    )

    imai = models.CharField(verbose_name="IMEI", max_length=20)
    serial_number = models.CharField(verbose_name="Серийный номер", max_length=20)

    def __str__(self):
        return self.serial_number