Django Rest-Framework nested serializer order

Question

Is there a way to order a nested serializer _set, for example order by pk or time-stamp.

So basically order song_set shown in the json data below from the most recent to the latest object created, in this case by order_by('-timestamp') or order_by('-pk').

Json data

{
    "pk": 151,
    "album_name": "Name",
    "song_set": [
         {
           pk: 3,
           timestamp: '5 seconds'
         },
         {
           pk: 2,
           timestamp: '10 seconds'
         },
         {
           pk: 1,
           timestamp: '15 seconds'
         }
    ]
}

Model

class Album(models.Model):
    album_name     = models.CharField(max_length=100, blank=True)


class Song(models.Model):
    album          = models.ForeignKey('album.Album', default=1)
    timestamp      = models.DateTimeField(auto_now_add=True, auto_now=False)

Serializer

class SongListSerializer(HyperlinkedModelSerializer):
    class Meta:
        model = Song
        fields = [
            'pk',
            'timestamp'
        ]

class AlbumSerializer(HyperlinkedModelSerializer):
    song_set = SongListSerializer(many=True, read_only=True)
    class Meta:
        model = Album
        fields = [
            'pk',
            'timestamp',
            'song_set'
        ]

Asked By: laa

||

Source

Answer 1

You can use SerializerMethodField and write custom method for this.

class AlbumSerializer(HyperlinkedModelSerializer):
    song_set = serializers.SerializerMethodField()
    class Meta:
        model = Album
        fields = [
            'pk',
            'timestamp',
            'song_set'
        ]

    def get_song_set(self, instance):
        songs = instance.song_set.all().order_by('-timestamp')
        return SongListSerializer(songs, many=True).data

Answered By: Muhammad Hassan

Answer 2

Old thread, but because it’s still popping up on Google I want to share my answer as well. Try overwriting the Serializer.to_representation method. Now you can basically do whatever you want, including customising the sorting of your response. In your case:

class AlbumSerializer(HyperlinkedModelSerializer):
    song_set = SongListSerializer(many=True, read_only=True)
    class Meta:
        model = Album
        fields = [
            'pk',
            'timestamp',
            'song_set'
        ]

    def to_representation(self, instance):
        response = super().to_representation(instance)
        response["song_set"] = sorted(response["song_set"], key=lambda x: x["timestamp"])
        return response

Answered By: SaturnFromTitan

Answer 3

In your ViewSet, you can specify a queryset with a custom Prefetch object that you can filter and order as you like. Prefetching causes just one additional database query (instead of one per parent object when using SerializerMethodField), giving vastly improved performance.

from rest_framework import viewsets
from django.db.models import Prefetch

class AlbumViewSet(viewsets.ModelViewSet):
    queryset = Album.objects.prefetch_related(Prefetch('song_set',
        queryset=Song.objects.order_by('-timestamp')))

Answered By: Endre Both

Answer 4

Add ordering meta parameter to your Song model:

class Song(models.Model):
    album = models.ForeignKey('album.Album', default=1)
    timestamp = models.DateTimeField(auto_now_add=True, auto_now=False)

    class Meta:
        ordering = ['timestamp', 'pk']

Answered By: intramuros

Django Rest-Framework nested serializer order

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