CODEWITHSUNDEEP
pythondjangodjango-rest-framework
user7864923
user7864923

Reputation:

Django Rest Framework SerializerMethodField TypeError: "'RelatedManager' object does not support indexing"

I have two SerializerMethodFields on a serializer. One of them returns obj.somelist.count() fine. But where I am asking the other method to return obj.somelist[0] I'm getting a TypeError 'RelatedManager' object does not support indexing. Any advice is much appreciated. Here's some code:

class TripPlaceSerializer(serializers.ModelSerializer):

    class Meta:
        model = TripPlace
        fields = ('trip', 'place', )


class StopSerializer(serializers.ModelSerializer):

    class Meta:
        model = TripPlace
        fields = ('place', )
        depth = 1


class TripSerializer(serializers.ModelSerializer):
    stops = StopSerializer(read_only=True, many=True)
    stops_count = serializers.SerializerMethodField()
    car = CarSerializer(read_only=True, many=False)
    origin = serializers.SerializerMethodField()
    # final = serializers.SerializerMethodField()

    class Meta:
        model = Trip
        fields = ('id', 'name', 'owner', 'car', 'stops_count', 'stops', 'origin', )

    def get_stops_count(self, obj):
        return obj.stops.count()

    def get_origin(self, obj):
        return obj.stops.first()

Upvotes: 2

Views: 2553

Answers (1)

Moses Koledoye
Moses Koledoye

Reputation: 78556

obj.somelist is the RelatedManager for whatever the underlying relationship is, you can't index it directly. You should call the first method of the RelatedManager to get the first object:

def get_origin(self, obj):
    return obj.somelist.first()

Or you can index(or slice) a queryset of the manager using a different index different from 0:

def get_origin(self, obj):
    return obj.somelist.all()[ind]

Upvotes: 5

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