Alternative for StringRelatedField

Question

I am trying to get following user with their names instead of PrimaryKey, I tried to use StringRelatedField. It worked for GET request, but it does not allow to write. Could not find any alternatives for this. I want to get json result as this:

{
    "id": 1,
    "user": "admin",
    "following": "user_1"
}

I assume instead of using StringRelatedField I should redefine create in serializers, am I right?

model.py

class Follow(models.Model):
    user = models.ForeignKey(
        User, on_delete=models.CASCADE, related_name='follower'
    )
    following = models.ForeignKey(
        User, on_delete=models.CASCADE, related_name='following'
    )

    class Meta:
        constraints = [
            models.UniqueConstraint(
                fields=['user', 'following'],
                name='unique_user_following'
            )
        ]

    def __str__(self) -> str:
        return self.following

serializer.py

class FollowSerializer(serializers.ModelSerializer):
    user = serializers.SlugField(
        read_only=True,
        default=serializers.CurrentUserDefault()
    )
    # following = serializers.StringRelatedField()

    class Meta:
        model = Follow
        fields = ('id', 'user', 'following',)

        validators = [
            serializers.UniqueTogetherValidator(
                queryset=Follow.objects.all(),
                fields=('user', 'following',)
            )
        ]

    def validate_following(self, value):
        if value == self.context.get('request').user:
            raise serializers.ValidationError(
                'You can not follow yourslef!'
            )
        return value

views.py

class FollowViewSet(viewsets.ModelViewSet):
    serializer_class = FollowSerializer

    def get_queryset(self):
        new_queryset = Follow.objects.filter(user=self.request.user)
        return new_queryset

    def perform_create(self, serializer):
        serializer.save(user=self.request.user)

Answer 1

A SlugRelatedField allows to also perform a lookup when writing and thus retrieve in this case the user with the given username.

You thus can implement this as:

from django.contrib.auth import get_user_model

class FollowSerializer(serializers.ModelSerializer):
    user = serializers.SlugField(
        read_only=True,
        default=serializers.CurrentUserDefault()
    )
    following = serializers.SlugRelatedField(
        slug_field='username',
        queryset=get_user_model().objects.all()
    )

    class Meta:
        model = Follow
        fields = ('id', 'user', 'following',)
        # …
    
    # …

---

Note: It is normally better to make use of the settings.AUTH_USER_MODEL [Django-doc] to refer to the user model, than to use the User model [Django-doc] directly. For more information you can see the referencing the User model section of the documentation.