DRF Serializer custom create - django-rest-framework

Question

I don't know if I'm doing this the right way, but I'm having problems with saving some relations with DRF serializers.
Let's say I have a MessageBoard and some MessageBoardPosts
Post has a serializer like:
class MessageBoardPostSerializer(serializers.ModelSerializer):
class Meta:
model = MessageBoardPost
fields = '__all__'
I want to add a Post by posting to /api/messageBoards/[PK]/create_post/
To do this, I added an action to the MessageBoard Viewset:
#action(detail=True, methods=['post'], permission_classes=[MatchesMessageboardVisibility])
def create_post(self, request, pk=None):
# Messageboard to post to
messageBoard = MessageBoard.objects.get(pk=pk)
if messageBoard is not None:
serializer = MessageBoardPostSerializer(data=request.data)
serializer.is_valid(raise_exception=True)
serializer.save()
return Response(serializer.data)
Since MessageBoard is a required FK on a post, I get validation errors when creating the post in the viewset.
What's the best way to solve this?

Answer 1

Serializer (i assume that "message_board" is ForeignKey in MessageBoardPost model):
class MessageBoardPostSerializer(serializers.ModelSerializer):
# this is read only by default which means serializer will not require that field
message_board = serializers.StringRelatedField()
class Meta:
model = MessageBoardPost
fields = '__all__'
Viewset action:
#action(detail=True, methods=['post'], permission_classes=[MatchesMessageboardVisibility])
def create_post(self, request, pk=None):
# Messageboard to post to
messageBoard = get_object_or_404(MessageBoard, pk=pk)
serializer = MessageBoardPostSerializer(data=request.data)
serializer.is_valid(raise_exception=True)
# here you can pass data without validation directly to the save method
serializer.save(message_board=messageBoard)
return Response(serializer.data)
you should write your variables in snake_case style like "message_board" etc.
for more advanced crud you should make url like /api/message-boards/PK/posts/ where you will POST your posts and message_board should be prefetched in overrited initial method

Answer 2

You can pass the MessageBoard as context to the serializer:
views.py
from django.shortcuts import get_object_or_404
#action(detail=True, methods=['post'], permission_classes=[MatchesMessageboardVisibility])
def create_post(self, request, pk=None):
# Messageboard to post to
message_board = get_object_or_404(MessageBoard, pk=pk)
context = {'message_board': message_board}
serializer = MessageBoardPostSerializer(data=request.data, context=context)
serializer.is_valid(raise_exception=True)
serializer.save()
return Response(serializer.data)
serializers.py
class MessageBoardPostSerializer(serializers.ModelSerializer):
class Meta:
model = MessageBoardPost
fields = '__all__'
def create(self, validated_data):
post = MessageBoardPost(**validated_data)
post.message_board = self.context['message_board']
post.save()
return post