how to save foreign keys using django-rest-framework

Question

I'm new to Django and I'm trying to save Unit and current_user foreign keys in the database based pk obtained but every time I try doing so but run into two types of error serializers.is_valid() raises an exception error or the serializer returns "Invalid data. Expected a dictionary, but got Unit."

I have tried a very very ugly way of bypassing serializers by getting rid but i get ee8452a4-2a82-4804-a010-cf2f5a41e006 must be an instance of SavedUnit.unit.I have also tried saving the foreign key directly using SavedUnit.objects.create() without luck

model.py

class SavedUnit(models.Model):
    """
    Saving units for later models
    relationship with units and users
    """
    id = models.UUIDField(primary_key=True, default=hex_uuid, editable=False)
    unit = models.ForeignKey(Unit, on_delete=models.CASCADE)
    user = models.ForeignKey('accounts.User', on_delete=models.CASCADE, related_name='user')
    published_at = models.DateTimeField(auto_now_add=True)

serializers.py

class SavedSerializer(serializers.ModelSerializer):
    unit = UnitSerializer()
    class Meta:
        model = SavedUnit
        fields = [
            'id',
            'unit'
        ]

views.py

class SavedUnitView(APIView):
    """
    Query all the unites saved
    """
    @staticmethod
    def get_unit(request, pk):
        try:
            return Unit.objects.get(pk=pk)
        except Unit.DoesNotExist:
            return Response(status=status.HTTP_400_BAD_REQUEST)
    @staticmethod
    def post(request, pk):
        if request.user.is_authenticated:
            unit = get_object_or_404(Unit, id=pk)
            serializers = SavedSerializer(data=unit)
            if serializers.is_valid(raise_exception=True):
                created = SavedUnit.objects.get_or_create(
                    user=request.user,
                    unit=unit)
                return Response(status=status.HTTP_201_CREATED)
        return Response(status=status.HTTP_401_UNAUTHORIZED)
    def get(self, request):
        units = SavedUnit.objects.filter(user=self.request.user.id)
        try:
            serializers = SavedSerializer(units, many=True)
            return Response(serializers.data, status=status.HTTP_200_OK)
        except Unit.DoesNotExist:
            return Response(status=status.HTTP_500_INTERNAL_SERVER_ERROR)

Answer 1

Your code is using serializer only for validation, but it is possible use it to insert or update new objects on database calling serializer.save().

To save foreign keys using django-rest-framework you must put a related field on serializer to deal with it. Use PrimaryKeyRelatedField.

serializers.py

class SavedSerializer(serializers.ModelSerializer):
    unit_id = serializers.PrimaryKeyRelatedField(
        source='unit',
        queryset=Unit.objects.all()
    )
    unit = UnitSerializer(read_only=True)

    class Meta:
        model = SavedUnit
        fields = [
            'id',
            'unit_id',
            'unit'
        ]

views.py

class SavedUnitView(APIView):
    permission_classes = (permissions.IsAuthenticated,) # For not handling authorization mannually

    def post(request):
        serializer = SavedSerializer(data=request.data)
        serializer.is_valid(raise_exception=True)  # Trigger Bad Request if errors exist
        serializer.save(user=request.user)         # Passing the current user
        return Response(serializer.data, status=status.HTTP_201_CREATED)

Now, the id of the unit will be passed in the request body like this

POST /saved-units/
Accept: application/json
Content-Type: application/json
Authorization: Token your-api-token

{ 
    "unit_id": 5  # Id of an existing Unit
}