network_inventory/devices/models/warranty.py

from django.db import models

from core.models import Category
from core.utils import td_format

from .device import Device


class WarrantyType(Category):
    description = models.TextField()

    class Meta:
        verbose_name_plural = "Warranty Types"


class Warranty(models.Model):
    device = models.ForeignKey(Device, on_delete=models.CASCADE)
    valid_from = models.DateField()
    valid_until = models.DateField()
    warranty_type = models.ForeignKey(WarrantyType, models.SET_NULL,
                                      blank=True, null=True)

    def __str__(self):
        return str(self.device)

    class Meta:
        verbose_name_plural = "Warranties"

    @property
    def customer(self):
        return self.device.customer

    @property
    def duration_in_years(self):
        delta = self.valid_until - self.valid_from
        return td_format(delta)