Using Django-taggit with django-rest-framework, i&

Question

I'm trying to figure it out why when i submit my form, my tags are not saved in my db. Pretty new with the django-rest-framework and Django-taggit too, i think i'm doing something wrong :)

First, before making my API with the rest-framework, i was using a generic view (CreateView and UpdateView) to register/validate my event. It was working fine but i decided to go further and try to build an API since i'm using Angularjs now.

Now my model event is created but without my tag and i have some errors. I put some code and i'll describe my errors after.

events/models.py

class Event(models.Model):
[...]

    title = models.CharField(max_length=245, blank=False)
    description = models.TextField(max_length=750, null=True, blank=True)
    start = models.DateTimeField()
    end = models.DateTimeField()
    created_at = models.DateTimeField(editable=False)
    updated_at = models.DateTimeField(editable=False)
    slug = AutoSlugField(populate_from='title', unique=True, editable=False)
    expert = models.BooleanField(choices=MODE_EXPERT, default=0)
    home = models.BooleanField(choices=HOME, default=0)
    nb_participant = models.PositiveSmallIntegerField(default=1)
    price = models.PositiveSmallIntegerField(default=0)
    cancelled = models.BooleanField(default=0)

    user = models.ForeignKey(User, editable=False, related_name='author')
    address = models.ForeignKey('Address', editable=False, related_name='events')
    participants = models.ManyToManyField(User, related_name='participants', blank=True, editable=False,
                                      through='Participants')
    theme_category = models.ForeignKey('EventThemeCategory', unique=True, editable=False)

    tags = TaggableManager(blank=True)

    class Meta:
        db_table = 'event'

    def save(self, *args, **kwargs):
        if not self.pk:
            self.created_at = timezone.now()
        self.updated_at = timezone.now()
        super(Event, self).save(*args, **kwargs)
    [...]

i'm using the serializers.HyperlinkedModelSerializer.

api/serializer.py

from taggit.models import Tag

class TagListSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Tag
        fields = ('url', 'id', 'name')


class EventSerializer(serializers.HyperlinkedModelSerializer):
    address = AddressSerializer()
    user = UserSerializer(required=False)
    tags = TagListSerializer(blank=True)

    class Meta:
        model = Event
        fields = ('url', 'id', 'title', 'description', 'start', 'end', 'created_at', 'updated_at', 'slug', 'expert','home', 'nb_participant', 'price', 'address', 'user', 'theme_category', 'tags')
        depth = 1

api/views/tags_views.py

from rest_framework import generics
from api.serializers import TagListSerializer
from taggit.models import Tag


class TagsListAPIView(generics.ListCreateAPIView):
    queryset = Tag.objects.all()
    model = Tag
    serializer_class = TagListSerializer


class TagsDetailAPIView(generics.RetrieveUpdateDestroyAPIView):
    queryset = Tag.objects.all()
    model = Tag
    serializer_class = TagListSerializer

api/views/events_views.py

class EventListAPIView(generics.ListCreateAPIView):
    queryset = Event.objects.all()
    model = Event
    serializer_class = EventSerializer
    paginate_by = 100

    def pre_save(self, obj):
        """
        Set the object's owner, based on the incoming request.
        """
        obj.user = self.request.user
        return super(EventListAPIView, self).pre_save(obj)

api/urls.py

    url(r'^events/(?P<slug>[0-9a-zA-Z_-]+)/$', EventDetailAPIView.as_view(), name='event-detail'),

So first when i call /api/events/name-of-my-event the API send me the good resource with my tags on it. The GET method is working fine.

I was thinking that rest-framework follow the query set. So if i can get the resource with with all my tags why when i use POST my tags are not register ?

Actually i have two problems with the POST method:

• first one if i send a tag which i have already created, he send me an error saying that the tag must be unique. I understand that, i don't want to create a new one, i just want it to be linked with my object. I don't have this problem when i use the generic view (it's done by magic :) and all is working fine)
• Secondly, when i try to create a new tag, my new event is saved but without my tags. You can see the response received by angularjs for my tag... He send me the name of the tag but without id, url (hyperlinked). When i checked my db the tag has not been created.

I think i have to make a custom get_queryset(self) in my tags_views but i'm not sure. I'll will continue to investigate. If someone have already to that and have some advise, i'll be very API. Thanks.

Answer 1

meet the same question. But I just want to save the tag list directly by TaggableManager (without TagListSerializer and TagsListAPIView). My solution is:

class MyModel(models.Model):
    ...
    tags = TaggableManager(blank=True)

    def get_tags_display(self):
        return self.tags.values_list('name', flat=True)

class MyModelSerializer(serializers.HyperlinkedModelSerializer):
    ...
    tags = serializers.Field(source='get_tags_display') # more about: http://www.django-rest-framework.org/api-guide/fields#generic-fields
    ...

class MyModelViewSet(viewsets.ModelViewSet):
    ...
    def post_save(self, *args, **kwargs):
        if 'tags' in self.request.DATA:
            self.object.tags.set(*self.request.DATA['tags']) # type(self.object.tags) == <taggit.managers._TaggableManager>
        return super(MyModelViewSet, self).post_save(*args, **kwargs)

The post data of tags data will be ['tagA', 'tagB',...], the TaggableManager will handle it. Thx.

For DRF>3.1, you just need to override create and update in your ModelSerializer class:

class StringListField(serializers.ListField): # get from http://www.django-rest-framework.org/api-guide/fields/#listfield
    child = serializers.CharField()

    def to_representation(self, data):
        return ' '.join(data.values_list('name', flat=True)) # you change the representation style here.


class MyModelSerializer(serializers.ModelSerializer):
    tags = StringListField()

    class Meta:
        model = models.MyModel

    def create(self, validated_data):
        tags = validated_data.pop('tags')
        instance = super(MyModelSerializer, self).create(validated_data)
        instance.tags.set(*tags)
        return instance

    def update(self, instance, validated_data):
        # looks same as create method

Answer 2

I had a bunch of errors but i found a way to resolve my problem. Maybe not the best as i'm pretty new with all of this but for now it works.

I'll try to describe all my errors maybe it'll help someone.

First my angularjs send a json which match exatly the queryset

So for example with my model events below, angularjs send to the API:

Now let's begin with all my errors:

• "A tag with this name already exist"

When i re-use a tag i have this error. Don't know why because with a classic validation without the API, all is working fine.

• With a new tag nothing is saved too.

When i try to use a new tag on my event event model nothing is saved on the database. Angularjs received a response with the tag name but with an id of null (see the pitcure on my original question)

• "AttributeError: 'RelationsList' object has no attribute 'add'"

Now i'm trying to think that to register my tags i need to have an instance of event already created. Thanks to that i will be able to add my tag on it like it's describe in the doc.

apple.tags.add("red", "green", "fruit")

So i decided to add a post_save in my events_views.py:

class EventListAPIView(generics.ListCreateAPIView):
    queryset = Event.objects.all()
    model = Event
    serializer_class = EventSerializer
    paginate_by = 100

    def pre_save(self, obj):
        """
        Set the object's owner, based on the incoming request.
        """
        obj.user = self.request.user
        return super(EventListAPIView, self).pre_save(obj)

    def post_save(self, obj, created=False):
        print 'tags', self.request.DATA
        obj.tags.add(self.request.DATA['tags'])
        return super(EventListAPIView, self).post_save(obj)

But now as is said i have this error AttributeError: 'RelationsList' object has no attribute 'add'. Actually, it's obvious since obj.tags is a list of object and not the TaggableManager anymore.

So i decided to start over and send my tags not in 'tags' but in another custom property 'tagged' to avoid conflit with the TaggableManager.

• "TypeError: unhashable type: 'list'"

New error :) I found the solution with this django-taggit-unhashable-type-list

def post_save(self, obj, created=False):
    map(obj.tags.add, self.request.DATA['tagged'])
    return super(EventListAPIView, self).post_save(obj)

• "TypeError: unhashable type: 'dict'"

Now, i figured it out that the tags i sent are not well formatted. I changed it (on the angularjs side) to send an array like this ['jazz','rock'] instead of [object, object]. Stupid mistake from a beginner.

Now the magic happen, response received by angularjs is good:

Sorry for my english. I know it may not be the best solution and i will try to update it when i'll find another solution.

Answer 3

http://blog.pedesen.de/2013/07/06/Using-django-rest-framework-with-tagged-items-django-taggit/

With the release of the Django Rest Framework 3.0, the code for the TagListSerializer has changed slightly. The serializers.WritableField was depreciated in favour for serializers.Field for the creation of custom serializer fields such as this. Below is the corrected code for Django Rest Framework 3.0.

class TagListSerializer(serializers.Field):
    def to_internal_value(self, data):
        if type(data) is not list:
            raise ParseError("expected a list of data")
        return data

    def to_representation(self, obj):
        if type(obj) is not list:
            return [tag.name for tag in obj.all()]
        return obj

I now use https://github.com/glemmaPaul/django-taggit-serializer library.