network_inventory/src/devices/models/warranty.py

from django.db import models

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

from .device import Device


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

    class Meta:
        ordering = ["name"]
        verbose_name_plural = "Warranty Types"


class Warranty(models.Model):
    customer = models.ForeignKey(Customer, on_delete=models.CASCADE, blank=True)
    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 save(self, *args, **kwargs):
        self.customer = self.device.customer
        super(Warranty, self).save(*args, **kwargs)

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

    class Meta:
        ordering = ["customer"]
        verbose_name_plural = "Warranties"
        constraints = [
            models.CheckConstraint(
                check=models.Q(valid_from__lte=models.F("valid_until")),
                name="valid_from_lt_valid_until",
            ),
        ]

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