Django DRF nested serializers are not linked

Question

I'm trying to build an API for a picture gallery using Django and Django Rest Framework for the API.

I have set up the following two models:

class Album(models.Model):
    name = models.CharField(max_length=100)
    description = models.TextField(null=True, blank=True)
    start_date = models.DateField()
    end_date = models.DateField(null=True, blank=True)
    parent_album = models.ForeignKey('self',
                                     null=True,
                                     blank=True,
                                     on_delete=models.CASCADE
                                    )

class Picture(models.Model):
    path = models.ImageField()
    album = models.ForeignKey('Album', on_delete=models.CASCADE)

For the serializers, I have defined the following, using the official Django DRF doc :

class PictureSerializer(serializers.ModelSerializer):

    class Meta:
        model = Picture
        fields = '__all__'


class AlbumSerializer(serializers.ModelSerializer):
    pictures = PictureSerializer(many=True, read_only=True)

    class Meta:
        model = Album
        fields = '__all__'

Now, I have some objects already defined, so I wanted to try in a shell:

>>> album = Album.objects.get(pk=1)
>>> len(Picture.objects.filter(album__exact=Album.objects.get(pk=1)))
3
>>> AlbumSerializer(instance=album).data
{'id': 1, 'name': 'First album', 'description': '', 'start_date': '2019-08-15', 'end_date': None, 'parent_album': None}
>>> AlbumSerializer()
AlbumSerializer():
    id = IntegerField(label='ID', read_only=True)
    pictures = PictureSerializer(many=True, read_only=True):
        id = IntegerField(label='ID', read_only=True)
        path = ImageField(max_length=100)
        album = PrimaryKeyRelatedField(queryset=Album.objects.all())
    name = CharField(max_length=100)
    description = CharField(allow_blank=True, allow_null=True, required=False, style={'base_template': 'textarea.html'})
    start_date = DateField()
    end_date = DateField(allow_null=True, required=False)
    parent_album = PrimaryKeyRelatedField(allow_null=True, queryset=Album.objects.all(), required=False)

You will notice that there are no pictures in the serialized data, but the field is there when I print the serializer, and that's my problem... Have I missed something somewhere?

Thanks for the help!

Answer 1

Your problem is due to the related name given to ForeignKeys.

Right now with the code you provided the name backwards relation name should be picture_set . So for the serializer to work you should change it do the following:

class AlbumSerializer(serializers.ModelSerializer):
    picture_set = PictureSerializer(many=True, read_only=True)

    class Meta:
        model = Album
        fields = '__all__'

But, if you want to display as pictures you can also do the following:

class AlbumSerializer(serializers.ModelSerializer):
    pictures = PictureSerializer(many=True, read_only=True, source='picture_set')

    class Meta:
        model = Album
        fields = '__all__'

Finally, if you want to get rid of the picture_set you should change your code to the following:

models.py

class Picture(models.Model):
    path = models.ImageField()
    album = models.ForeignKey('Album', on_delete=models.CASCADE, related_name='pictures')

serializers.py

class AlbumSerializer(serializers.ModelSerializer):
    pictures = PictureSerializer(many=True, read_only=True)

    class Meta:
        model = Album
        fields = '__all__'