Estoy agregando el campo 'agregado' para verificar a qué categorías se agrega la Publicación del usuario (Conjunto). Suena horrible, así que vamos a sumergirnos en el código.

Quiero optimizar la función get_categories (self, obj).

class CategorySerializer(serializers.ModelSerializer):
    added = serializers.BooleanField()
    class Meta:
        model = Category
        fields = (
            'id',
            'name',
            'added'
        )


class OutfitDetailSerializer(serializers.ModelSerializer):

    def get_categories(self, obj):
        user = self.context['request'].user
        categories = Category.objects.filter(owner=user)
        added = categories.extra(select={'added': '1'}).filter(outfits__pk=obj.pk)
        added = list(added.values('added', 'name', 'id'))
        added_f = categories.extra(select={'added': '0'}).exclude(outfits__pk=obj.pk)
        added_f = list(added_f.values('added', 'name', 'id'))
        categories = added + added_f
        return CategorySerializer(categories, many=True).data

¡La salida está abajo!

"categories": [{
        "id": 1,
        "name": "Gym",
        "added": true
    }, {
        "id": 2,
        "name": "School",
        "added": false
    }, {
        "id": 3,
        "name": "hollymo",
        "added": true
    }, {
        "id": 4,
        "name": "Normal",
        "added": false
    }, {
        "id": 6,
        "name": "New Category",
        "added": false
    }
]

Aquí está models.py

class Outfit(models.Model):
    ...
    user = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True)
    content = models.CharField(max_length=30)
    ...

class Category(models.Model):
    name = models.CharField(max_length=20)
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True)
    outfits = models.ManyToManyField(Outfit, related_name="categories", blank=True)
    main_img = models.ImageField(
                            upload_to=upload_location_category,
                            null=True,
                            blank=True)
    ...

aquí elrepositorio para prueba