DRF many-to-one reverse lookup

Question

I have an API endpoint returning pets and their owners.

• Each owner has a name and one or more pets
• Each pet has a name and one owner

Example Django models:

class Owner(models.Model):
    name = models.CharField(max_length=200)

class Pet(models.Model):
    owner = models.ForeignKey(Owner, on_delete=models.CASCADE)
    name = models.CharField(max_length=200)

I've configured my API to return JSON data like this:

[
    {
        "id": 2,
        "name": "Scotch",
        "owner": {
            "id": 2,
            "name": "Ben"
        }
    },
    {
        "id": 3,
        "name": "Fluffy",
        "owner": {
            "id": 1,
            "name": "Fred"
        }
    },
    {
        "id": 1,
        "name": "Spot",
        "owner": {
            "id": 1,
            "name": "Fred"
        }
    }
]

Example DRF serializers:

class OwnerSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Owner
        fields = ("id", "name")

class PetSerializer(serializers.HyperlinkedModelSerializer):
    owner = OwnerSerializer()
    class Meta:
        model = Pet
        fields = ("id", "name", "owner")

While that's all fine and dandy, I'd actually like to have an endpoint that returns a list of owners and their pets. So I'd get this data instead:

[
    {
        "id": 1,
        "name": "Fred",
        "pets": [
            { "id": 1, "name": "Spot" },
            { "id": 3, "name": "Fluffy" }
        ]
    },
    {
        "id": 2,
        "name": "Ben",
        "pets": [
            { "id": 2, "name": "Scotch" }
        ]
    }
]

How can I achieve that output?

Answer 1

You need to add pet_set field to OwnerSerializer like this:

class PetSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Pet
        fields = ("id", "name")

class OwnerSerializer(serializers.HyperlinkedModelSerializer):
    pet_set = PetSerializer(many=True, read_only=True)
    class Meta:
        model = Owner
        fields = ("id", "name", "pet_set")

This will work bacause many-to-one relation default reverse lookup name is <model>_set or pet_set in your case. You can change it by using related_name:

class Pet(models.Model):
    owner = models.ForeignKey(Owner, related_name='pets', on_delete=models.CASCADE)

In this case you can use pets name inside serializer:

class OwnerSerializer(serializers.HyperlinkedModelSerializer):
    pets = PetSerializer(many=True, read_only=True)

Now in OwnerListView you can use this new serializer:

class OwnerListView(ListAPIView):
    queryset = Owner.objects.all()
    serializer_class = OwnerSerializer