Django @transaction.atomic() to prevent creating objects in concurrency

[Aamu Padi]

I have a ticket model, and its ticket serialiazer. The ticket model has a bought and a booked_at field. And also a unique_together attribute for show and seat.

class Ticket(models.Model):

    show = models.ForeignKey(Show, on_delete=models.CASCADE)

    seat = models.ForeignKey(Seat, on_delete=models.CASCADE)

    user = models.ForeignKey(User, on_delete=models.CASCADE)

    booked_at = models.DateTimeField(default=timezone.now)

    bought = models.BooleanField(default=False)

    class Meta:

        unique_together = ('show', 'seat')

• On the ticket serializer, the serializer on validation checks whether the ticket was bought or not.
  
• If it is bought, then it will raise an error.
• If its not bought then Check if the ticket was booked within 5 minutes.
• If its booked within 5 minutes, then raise an error.
• Else if the booked time is more than 5 minutes, than delete the old ticket and return valid.

TicketSerializer:

class TicketSerializer(serializers.Serializer):

    seat = serializers.PrimaryKeyRelatedField(queryset=Seat.objects.all())

    show = serializers.PrimaryKeyRelatedField(queryset=Show.objects.all())

    user = serializers.PrimaryKeyRelatedField(queryset=User.objects.all())

    bought = serializers.BooleanField(default=False)

    def validate(self, attrs):

        if attrs['seat']:

            try:

                ticket = Ticket.objects.get(show=attrs['show'], seat=seat)

                if not ticket.bought:

                    if ticket.booked_at < timezone.now() - datetime.timedelta(minutes=5):

                        # ticket booked crossed the deadline

                        ticket.delete()

                        return attrs

                    else:

                        # ticket in 5 mins range

                        raise serializers.ValidationError("Ticket with same show and seat exists.")

                else:

                    raise serializers.ValidationError("Ticket with same show and seat exists.")

            except Ticket.DoesNotExist:

                return attrs

        else:

            raise serializers.ValidationError("No seat value provided.")

On the view, I am using @transaction.atomic() to make sure the ticket/s are created only if all of them are valid, or don't create ANY ticket if not valid.

@transaction.atomic()

@list_route(

    methods=['POST'],

)

def book_tickets_by_show(self, request, show_id=None):

    try:

        show = Show.objects.get(id=show_id)

        user = request.user

        ...

        ...

        data_list = [...]

        with transaction.atomic():

            try:

                serializer = TicketSerializer(data=data_list, many=True)

                if serializer.is_valid():

                    serializer.save()

                    ....

                return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

            except (Seat.DoesNotExist, ValueError, ConnectionError) as e:

                return Response({'detail': str(e)}, status=status.HTTP_400_BAD_REQUEST)

    except (Show.DoesNotExist, IntegrityError) as e:

        return Response({'detail': str(e)}, status=status.HTTP_400_BAD_REQUEST)

What I would like to know is will it help in preventing when more than one requests are called for creating the ticket/s for same seat/s?

Suppose, User A wants to book ticket with seat 5,6 and User B wants to book ticket with seat 3,6, and another User C wants to book the ticket with seats 2,3,4,5,6. Will the above method prevent booking tickets for their respective seats for all the users, and only create tickets for one user (maybe whose transaction was first)? Or if there is a better way then could you please advice me how to. I hope I was clear. If not please ask.

Thank you