old_contents: from .models import Schedule, MessageSet, Message, BinaryContent
  from rest_framework.viewsets import ModelViewSet
  from rest_framework.permissions import IsAuthenticated
  from .serializers import (ScheduleSerializer, MessageSetSerializer,
                            MessageSerializer, BinaryContentSerializer,
                            MessageListSerializer, MessageSetMessagesSerializer)
  
  
  class ScheduleViewSet(ModelViewSet):
  
      """
      API endpoint that allows Schedule models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = Schedule.objects.all()
      serializer_class = ScheduleSerializer
  
  
  class MessageSetViewSet(ModelViewSet):
  
      """
      API endpoint that allows MessageSet models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = MessageSet.objects.all()
      serializer_class = MessageSetSerializer
  
  
  class MessageViewSet(ModelViewSet):
  
      """
      API endpoint that allows Message models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = Message.objects.all()
      serializer_class = MessageSerializer
      filter_fields = ('messageset', 'sequence_number', 'lang', )
  
  
  class BinaryContentViewSet(ModelViewSet):
  
      """
      API endpoint that allows BinaryContent models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = BinaryContent.objects.all()
      serializer_class = BinaryContentSerializer
  
  
  class MessagesContentView(ModelViewSet):
  
      """
      A simple ViewSet for viewing more detailed message content.
      """
      permission_classes = (IsAuthenticated,)
      queryset = Message.objects.all()
      serializer_class = MessageListSerializer
  
  
  class MessagesetMessagesContentView(ModelViewSet):
  
      """
      API endpoint that allows MessageSet models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = MessageSet.objects.all()
      serializer_class = MessageSetMessagesSerializer
  
new_contents: from .models import Schedule, MessageSet, Message, BinaryContent
  from rest_framework.viewsets import ModelViewSet
  from rest_framework.permissions import IsAuthenticated
  from .serializers import (ScheduleSerializer, MessageSetSerializer,
                            MessageSerializer, BinaryContentSerializer,
                            MessageListSerializer, MessageSetMessagesSerializer)
  
  
  class ScheduleViewSet(ModelViewSet):
  
      """
      API endpoint that allows Schedule models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = Schedule.objects.all()
      serializer_class = ScheduleSerializer
  
  
  class MessageSetViewSet(ModelViewSet):
  
      """
      API endpoint that allows MessageSet models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = MessageSet.objects.all()
      serializer_class = MessageSetSerializer
      filter_fields = ('short_name', 'content_type', )
  
  
  class MessageViewSet(ModelViewSet):
  
      """
      API endpoint that allows Message models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = Message.objects.all()
      serializer_class = MessageSerializer
      filter_fields = ('messageset', 'sequence_number', 'lang', )
  
  
  class BinaryContentViewSet(ModelViewSet):
  
      """
      API endpoint that allows BinaryContent models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = BinaryContent.objects.all()
      serializer_class = BinaryContentSerializer
  
  
  class MessagesContentView(ModelViewSet):
  
      """
      A simple ViewSet for viewing more detailed message content.
      """
      permission_classes = (IsAuthenticated,)
      queryset = Message.objects.all()
      serializer_class = MessageListSerializer
  
  
  class MessagesetMessagesContentView(ModelViewSet):
  
      """
      API endpoint that allows MessageSet models to be viewed or edited.
      """
      permission_classes = (IsAuthenticated,)
      queryset = MessageSet.objects.all()
      serializer_class = MessageSetMessagesSerializer
  
subject: Update filter. Review by @nicolaasdiebaas