How to properly save a ManyToManyField in DRF

[dsaltyfrere]

I have a published_item model which has assignable categories. For some reason I'm only able to save one of the categories but I believe i'm doing something wrong.

My PublishedItemViewSet looks as follows

class PublishedItemViewSet(viewsets.ModelViewSet):
    queryset = PublishedItem.objects.all()
    serializer_class = PublishedItemSerializer
    permission_classes = [permissions.AllowAny]

    def create(self, request):
        """
        Create a published_item
        """
        serializer = PublishedItemSerializer(data=request.data, context={'request': request})
        if serializer.is_valid(raise_exception=ValueError):
            user = request.user
            published_item = serializer.create(validated_data=request.data, user=user)
            try:
                ...
                some django_channels stuff
                ....
                return Response(serializer.data, status=status.HTTP_201_CREATED)
            except Exception as e:
                print(e)
                return Response(serializer.error_messages, status=status.HTTP_400_BAD_REQUEST)
        return Response(serializer.error_messages, status=status.HTTP_400_BAD_REQUEST)

The PublishedItemSerializer is

class PublishedItemSerializer(serializers.HyperlinkedModelSerializer):
    published_by = serializers.SlugRelatedField(many=False, read_only=True, slug_field='username')

    category = serializers.SlugRelatedField(many=True, slug_field='name', queryset=Category.objects.all())

    class Meta:
        model = PublishedItem
        fields = '__all__'

    def create(self, validated_data, user):
        try:
            published_item = PublishedItem.objects.create(
                text = validated_data['text'],
                url = validated_data['url'],
                photo = validated_data['photo'],
                published_by = user,
            )
            published_item.save()
            category = Category.objects.get(name=validated_data["category"])
            published_item.category.add(category)
            return published_item
        except Exception as e:
            print(traceback.format_exc())
            print(e)

My PublishedItem model:

from django.db import models
from django.utils.timezone import now
from django.contrib.auth.models import User
from api.models.category import Category
from api.validators.published_item_validator import validate_published_item_url
from api.utils.path_and_rename_file import path_and_rename
from unfolded_rest_api.settings import MEDIA_ROOT


class PublishedItem(models.Model):
    text = models.TextField()
    url = models.CharField(max_length=256, validators=[validate_published_item_url])
    photo = models.ImageField(blank=True, null=True, upload_to=path_and_rename)
    published_at = models.DateTimeField(default=now, editable=False)
    updated_at = models.DateTimeField(blank=True, default=now)
    published_by = models.ForeignKey(User, on_delete=models.DO_NOTHING, related_name='author')
    category = models.ManyToManyField(Category, related_name='categories')


    def __str__(self) -> str:
        return f"{self.text}\n{self.url}\n{self.published_at}:{self.updated_at}\n{self.published_by}"

My Category model:

from django.db import models

class Category(models.Model):
    name = models.CharField(max_length=128, unique=True)

    def __str__(self) -> str:
        return self.name

If I check the incoming validated_data I have the following
<QueryDict: {'csrfmiddlewaretoken': ['PYA5owmCTSsuuqqTG2D0OySwalZD0D88PZT7Ft0NqwxPnsAhmTUdH1dV1e0SXiyz'], 'url': ['https://www.reuters.com/search/news?sortBy=date&dateRange=all&blob=cryptocurrencies'], 'category': ['elliptic', 'another category', 'third category'], 'text': ['test'], 'photo': [''], 'updated_at': ['']}>

So I should be able to do

for category in validated_data["category"]:
    c = Category.objects.get(name=category)
    published_item.category.add(c)

However, the incoming validated_data["category"] is a string and not a list, when I attempt to iterate over this object i'm receiving single chars rather than the full category name.

What am I doing wrong, how do I properly save ManyToMany relations in DRF?

[nbeaulat]

Same problem... Have you found a solution?