uday12kumar

class Slot(models.Model): 
	id = models.AutoField(primary_key=True,)
	user = models.ForeignKey(User)   
	seats= models.IntegerField(default=10)

uday12kumar

def book(self, seats_selected,slot_id):
	if self.seats < self.seats_selected:
		raise errors.InsufficientSeats() 
	self.seats -= seats_selected
	self.save()


def cancel_booking(self, seats_selected):
 	self.seats += seats_selected
 	self.save()

uday12kumar

@classmethod
def cancel(cls, id, seats_selected):
	with transaction.atomic():
		slot= (cls.objects.select_for_update().get(id=id))
		slot.seats += seats_selected
		slot.save()
		return slot

uday12kumar

@classmethod
def book(cls, id, seats_selected): 
	with transaction.atomic():
		if seats < self.seats_selected:
			raise errors.InsufficientSeats() 
		slot = (cls.objects.select_for_update().get(id=id))
		slot.seats -= seats_selected
		slot.save() 
		return slot