Use a related field in lookup_field in Django REST framework

Question

I have a user model and a profile model that is created automatically when a user is registered. In my view for retrieving the user profile, I am trying to get the user profile using the username but DRF uses pk by default. So I added a lookup field with the username but DRF can't seem to resolve it:

my profile model:

class Profile(TimeStampedModel):
    user = models.OneToOneField('User', on_delete=models.CASCADE, related_name='customer_profile')
    bio = models.TextField(blank=True)
    image = models.URLField(blank=True)
    
    def __str__(self):
        return self.user.username

my profile serializer :

class ProfileSerializer(serializers.ModelSerializer):
    username = serializers.StringRelatedField(source='user.username', read_only=True)
    bio = serializers.CharField(allow_blank=True, allow_null=True)
    image = serializers.SerializerMethodField()
    
    class Meta:
        model = Profile
        fields = ['username', 'bio', 'image']
        
    def get_image(self, obj):
        if obj.image:
            return obj.image
        
        return 'https://static.productionready.io/images/smiley-cyrus.jpg'

my profile retrieving view :

class ProfileRetrieveAPIView(generics.RetrieveAPIView):
    queryset = Profile.objects.all()
    serializer_class = ProfileSerializer
    lookup_field = 'username'


    def retrive(self, request, username, *args, **kwargs):
        
        try:
            profile = Profile.objects.select_related('user').get(
                user__username = username
            )
        except Profile.DoesNotExist:
            ProfileDoesNotExist
        
        serializer = self.serializer_class(profile)
        
        return Response(serializer.data, status=status.HTTP_200_OK)

my profile endpoint:

urlpatterns = [ 
    # ....
    path('profiles/<str:username>', views.ProfileRetrieveAPIView.as_view()),
]

I am getting the error:

Cannot resolve keyword 'username' into field. Choices are: bio, created_at, id, image, updated_at, user, user_id

What am I doing wrong?

Answer 1

Use nested serialzer.

class UserSerializer(serializers.ModelSerializer):
class Meta:
    model = User
    fields = ('username',)

And in your profile serializer:

  username = UserSerializer(many=False, read_only=True)

Answer 2

You can use this

class ProfileSerializer(serializers.ModelSerializer):
    username = serializers.CharField(source='user.username', read_only=True)
    bio = serializers.CharField(allow_blank=True, allow_null=True)
    image = serializers.SerializerMethodField()
    
    class Meta:
        model = Profile
        fields = ['username', 'bio', 'image']
        
    def get_image(self, obj):
        if obj.image:
            return obj.image
        
        return 'https://static.productionready.io/images/smiley-cyrus.jpg'