插入多对多字段 Django

Question

I'm trying to build Reddit in Django and for that, I am creating a board where users can discuss topics. But I am not able to map user and board.

Model:

class Board(models.Model):
    id = models.AutoField(primary_key=True)
    unique_id = models.CharField(max_length=100, null=False, unique=True)
    created_by = models.ForeignKey(User_Detail, on_delete=models.CASCADE, related_name="board_creator")
    name = models.CharField(max_length=100, null=False, unique=
True)


class UserBoardMapping(models.Model):
    user = models.ManyToManyField(User_Detail)
    board = models.ManyToManyField(Board)
    user_type = models.CharField(max_length=10, choices=USER_TYPE, default='moderator')

My view:

class CreateBoard(APIView):
    def post(self, request):
      data = JSONParser().parse(request)
      unique_id = data.get('board_id', None)
      created_by = data.get('created_by', None)
      name = data.get('name', None)

    if not created_by or not name:
        return Response({'ERROR': 'Please provide both username and password'},
                        status=status.HTTP_400_BAD_REQUEST)

    if Board.objects.filter(name=name).exists():
        return JsonResponse({'ERROR': "Board Already registered! "},
                            status=status.HTTP_409_CONFLICT)

    if not User_Detail.objects.filter(username=created_by).exists():
        return JsonResponse({'ERROR': "Username is not registered! "},
                            status=status.HTTP_404_NOT_FOUND)

    username = User_Detail.objects.get(username=created_by)
    board = Board(unique_id=unique_id, created_by=username, name=name)
    board.save()

    user_board_mapping = UserBoardMapping(user=username, board=board)
    user_board_mapping.save()

error:

Direct assignment to the forward side of a many-to-many set is prohibited. Use user.set() instead.

UserBoardMapping is not working, how can I map user and board and Insert data in many to many field what am I doing wrong here in this code?

Answer 1

For your UserBoardMapping, user and board are M2M fields. Because of that, you have to use .set() like in your error message. You can also use .add() if you want to add a value, like in your example.

user_board_mapping = UserBoardMapping.objects.create(user_type='whatyouwant')
user_board_mapping.user.add(username)
user_board_mapping.board.add(board)

You can find here some examples: https://docs.djangoproject.com/en/3.1/topics/db/examples/many_to_many/#many-to-many-relationships