cara menyelesaikan maslah ini (help missing 1 required positional argument)

class OrderItem(models.Model):
    order = models.ForeignKey('Order', related_name='items')
    product = models.ForeignKey('Product', related_name='order_items')
    price = models.DecimalField(max_digits=10, decimal_places=2)
    quantity = models.PositiveIntegerField(default=1)

help missing 1 required positional argument = 'on_delete'