class Item(models.Model):
    name = models.CharField(max_length=120)
    price = models.DecimalField(max_digits=6, decimal_places=2)
    description = models.TextField(blank=True)
    rating = models.IntegerField(default=0, editable=False)
    images = models.ManyToManyField('Picture', related_name='item_images')

    def save(self, *args, **kwargs):
        if Review.objects.filter(item_id=self.id):
            self.rating = Review.objects.filter(item_id=self.id).aggregate(Avg('rating'))['rating__avg']
        super(Item, self).save(*args, **kwargs)


class Review(models.Model):
    ratings = (
        (1, '1'),
        (2, '2'),
        (3, '3'),
        (4, '4'),
        (5, '5'),
    )

    user = models.ForeignKey(AUTH_USER_MODEL, null=True, on_delete=models.SET_NULL)
    item = models.ForeignKey('items.Item', on_delete=models.CASCADE)
    text = models.TextField()
    rating = models.IntegerField(choices=ratings)

    def __str__(self):
        return 'Review #{} from {}'.format(self.id, self.user.username)