Django Rest Framework: How serialize list of list?

Question

How to serialize list of list of Floats using Django Rest serializers?

My data is (repr of my list of object):

[{
    'id': '413',
    'data': [
        [None, 32.33125, None, None],
        [None, 37.96, 48.70112359550562, 66.118],
        [None, None, 58.06576923076923, 77.31023809523809],
        [None, None, None, 110.0075],
        [None, None, None, 139.89]
    ]
}, {
    'id': '406',
    'data': [
        [None, 35.33125, None, None],
        [None, 37.96, 43.123, 66.118],
        [None, None, 58.12, 72,123],
        [None, None, None, 119.000234],
        [None, None, None, 139.89]
    ]
}]

For users trying to propose different approach, I need to explain that I need serializer class because I want to use generics.ListAPIView and I need to setup serializer_class property.

WBAR · Accepted Answer · 2015-08-25 22:31:24Z

You must create Field class that will work with Null values:

class FixedFloatField(serializers.FloatField):
    def to_internal_value(self, data):
        if data is None:
            return data
        return super().to_internal_value(data)

    def to_representation(self, value):
        if value is None:
            return value
        return super().to_representation(value)

(because standard one throws TypeError: float() argument must be a string or a number, not 'NoneType')

Now use this Serializer (the trick is to use ListField):

class SearchResultSerializer(serializers.Serializer):
    id = serializers.IntegerField()
    data = serializers.ListField(
        child=serializers.ListField(
            child=FixedFloatField(
                allow_null=True,
                required=False,
                default=None
            )
        )
    )

Daniel Albarral · Accepted Answer · 2016-12-29 19:58:11Z

1

You can use the biult-in json module.

data = [{
    'id': '413',
    'data': [
        [None, 32.33125, None, None],
        [None, 37.96, 48.70112359550562, 66.118],
        [None, None, 58.06576923076923, 77.31023809523809],
        [None, None, None, 110.0075],
        [None, None, None, 139.89]
    ]
}, {
    'id': '406',
    'data': [
        [None, 35.33125, None, None],
        [None, 37.96, 43.123, 66.118],
        [None, None, 58.12, 72,123],
        [None, None, None, 119.000234],
        [None, None, None, 139.89]
    ]
}]

import json
json_data = json.dumps(data)

You can mix this with a DRF view:

from rest_framework.response import Response
...
json_data = json.dumps(data)
return Response(json_data)

EDIT

To use ListAPIView

assuming your data are coming from a model named Mymodel

# Serializer
from rest_framework import serializers

class MymodelSerializer(serializers.ModelSerializer):

    class Meta:
        model = Mymodel

# View
from rest_framework import generics

class MymodelList(generics.ListAPIView):

    queryset = Mymodel.objects.filter(whatever=whatever)

    def list(self, request):
        # Note the use of `get_queryset()` instead of `self.queryset`
        queryset = self.get_queryset()
        serializer = UserSerializer(queryset, many=True)
        return Response(serializer.data)

Taken from DRF docs

edited Dec 29, 2016 at 19:58

Daniel Albarral

4526 silver badges12 bronze badges

answered Aug 25, 2015 at 22:06

Gocht

10.3k3 gold badges48 silver badges84 bronze badges

6 Comments

WBAR Over a year ago

I want to use generics.ListAPIView so I need to setup serializer_class propherty

Gocht Over a year ago

You didn't specified.

WBAR Over a year ago

that's why You gave me -1 ?

Gocht Over a year ago

from DRF docs: Used for read-only endpoints to represent a collection of model instances. So the serializer you will use in the view is the same serializer tu return an only object. But you will be able to define a queryset to filter resulting objects if needed.

WBAR Over a year ago

You making to much assumptions, this object is not from Model instance

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