[FIXED] Is there an elegant way to flatten nested JSON with a django serializer?

Issue

I receive nested JSON from an API (I can't influence the structure). I want to flatten the nested fields while deserializing an object, using a django rest framework serializer. How do I do this elegantly?

Here is my current approach, which works by using nested serializers and doing the flattening in the .create():

from dataclasses import dataclass

from rest_framework import serializers

input_data = {
    "objectName": "Johnny",
    "geoInfo": {
        "latitude": 1.2,
        "longitude": 3.4,
    },
}

flattened_output = {
    "name": "Johnny",
    "lat": 1.2,
    "lon": 3.4,
}


@dataclass
class Thing:
    name: str
    lat: float
    lon: float


class TheFlattener(serializers.Serializer):
    class GeoInfoSerializer(serializers.Serializer):
        latitude = serializers.FloatField()
        longitude = serializers.FloatField()

    objectName = serializers.CharField(max_length=50, source="name")
    geoInfo = GeoInfoSerializer()

    def create(self, validated_data):
        geo_info = validated_data.pop("geoInfo")
        validated_data["lat"] = geo_info["latitude"]
        validated_data["lon"] = geo_info["longitude"]
        return Thing(**validated_data)


serializer = TheFlattener(data=input_data)
serializer.is_valid(raise_exception=True)
assert serializer.save() == Thing(**flattened_output)

I know that when serializing objects to JSON, you can reference nested/related objects in the source parameter e.g.

first_name = CharField(source="user.first_name")

which is really nice, but I haven't been able to find something similar for deserialization.

Solution

Credit to this thread for providing the answer: source="*" flattens nested fields into the validated_data.

In this case, the solution looks like this:

class TheFlattener(serializers.Serializer):
    class GeoInfoSerializer(serializers.Serializer):
        latitude = serializers.FloatField(source="lat")  # rename here
        longitude = serializers.FloatField(source="lon")

    objectName = serializers.CharField(max_length=50, source="name")
    geoInfo = GeoInfoSerializer(source="*")  # unpack nested fields here

    def create(self, validated_data):  
        return Thing(**validated_data)

Answered By - binnev