django-rest-framework, multitable model inheritance, ModelSerializers and nested serializers

django, django-models, django-rest-framework, python

Solution

I've solved this issue a slightly different way.

Using:

- DRF 3.5.x

- django-model-utils 2.5.x

My `models.py` look like this:

class Person(models.Model):
    first_name = models.CharField(max_length=40, blank=False, null=False)
    middle_name = models.CharField(max_length=80, blank=True, null=True)
    last_name = models.CharField(max_length=80, blank=False, null=False)
    family = models.ForeignKey(Family, blank=True, null=True)


class Clergy(Person):
    category = models.IntegerField(choices=CATEGORY, blank=True, null=True)
    external = models.NullBooleanField(default=False, null=True)
    clergy_status = models.ForeignKey(ClergyStatus, related_name="%(class)s_status", blank=True, null=True)


class Religious(Person):
    religious_order = models.ForeignKey(ReligiousOrder, blank=True, null=True)
    major_superior = models.ForeignKey(Person, blank=True, null=True, related_name="%(class)s_superior")


class ReligiousOrder(models.Model):
    name = models.CharField(max_length=255, blank=False, null=False)
    initials = models.CharField(max_length=20, blank=False, null=False)


class ClergyStatus(models.Model):
    display_name = models.CharField(max_length=255, blank=True, null=True)
    description = models.CharField(max_length=255, blank=True, null=True)

Basically - The base model is the "Person" model - and a person can either be Clergy, Religious, or neither and simply be a "Person". While the models that inherit `Person` have special relationships as well.

In my `views.py` I utilize a mixin to "inject" the subclasses into the queryset like so:

class PersonSubClassFieldsMixin(object):

    def get_queryset(self):
        return Person.objects.select_subclasses()

class RetrievePersonAPIView(PersonSubClassFieldsMixin, generics.RetrieveDestroyAPIView):
    serializer_class = PersonListSerializer
    ...

And then real "unDRY" part comes in `serializers.py` where I declare the "base" PersonListSerializer, but override the `to_representation` method to return special serailzers based on the instance type like so:

class PersonListSerializer(serializers.ModelSerializer):

    def to_representation(self, instance):
        if isinstance(instance, Clergy):
            return ClergySerializer(instance=instance).data
        elif isinstance(instance, Religious):
            return ReligiousSerializer(instance=instance).data
        else:
            return LaySerializer(instance=instance).data

    class Meta:
        model = Person
        fields = '__all__'


class ReligiousSerializer(serializers.ModelSerializer):
    class Meta:
        model = Religious
        fields = '__all__'
        depth = 2


class LaySerializer(serializers.ModelSerializer):
    class Meta:
        model = Person
        fields = '__all__'


class ClergySerializer(serializers.ModelSerializer):
    class Meta:
        model = Clergy
        fields = '__all__'
        depth = 2

The "switch" happens in the `to_representation` method of the main serializer (`PersonListSerializer`). It looks at the instance type, and then "injects" the needed serializer. Since `Clergy`, `Religious` are all inherited from `Person` getting back a `Person` that is also a `Clergy` member, returns all the `Person` fields and all the `Clergy` fields. Same goes for `Religious`. And if the `Person` is neither `Clergy` or `Religious` - the base model fields are only returned.

Not sure if this is the proper approach - but it seems very flexible, and fits my usecase. Note that I save/update/create `Person` thru different views/serializers - so I don't have to worry about that with this type of setup.

Problem

Original source