gistfile1.txt

 def post(self, request):
        serializer = CompletedAchievementCreateSerializer(data=request.DATA)

        if serializer.is_valid():
            achievement = Achievement.objects.get(id=serializer.data['achievement'])
            stakeholder = Stakeholder.objects.get(id=serializer.data['stakeholder'])

            try:
                CompletedAchievement.objects.create(
                    achievement=achievement,
                    stakeholder=stakeholder)

                return Response(serializer.data, status=status.HTTP_201_CREATED) 
            except IntegrityError as e:
                return Response(status=status.HTTP_409_CONFLICT)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)