Django模型与Foreignkey模型重复

Question

I have two models, one to create a title and one to create a vote for this title.

When I create more than one vote on the same title, I get duplicate titles, and I can't figure out why.

Here is my vote model,

class Vote(GenericModel):
    """
    Model for vote on a title
    """
    title = models.ForeignKey(Title, blank=True, related_name='votes')

    user = models.ForeignKey(ArtLover, blank=True)

    def __str__(self):
        return _("vote on {}").format(self.title.__str__())

and the view to vote:

@detail_route(methods=['post'])
def vote(self, request, *args, **kwargs):
    """
    Create vote for a title
    """
    title = Title.objects.get(text=kwargs.get('text'))
    user = ArtLover.objects.get(id=request.user.id)

    if title.user.id == user.id:
        return Response(
            _("You can't vote for your own title"),
            status=status.HTTP_403_FORBIDDEN
        )

    if Vote.objects.filter(title=title, user=user).exists():
        return Response(
            _("Vote already exists"),
            status=status.HTTP_409_CONFLICT
        )

    vote = Vote.objects.create(title=title, user=user)

    return Response({
        'vote': VoteSerializer(vote).data
    }, status=status.HTTP_201_CREATED)

If I print the number of title instances after creating the vote, the count is good, no duplicate, so I assume the duplication happens later. Can you point me where/why the duplication happens?

When I delete the vote, the title created by the duplication is deleted as well.

Edit 1 :

I have tried to create a custom manager for the title models to block the duplication, but when the duplication happen while creating a vote, the title manager is not called.

When I compare the origin models instance primary key with the duplication they are the same.

Edit 2:

trying to order the titles fields in artworks serializer

my artworks serializer :

class ArtworkDetailSerializer(serializers.ModelSerializer):
    """
    Detailed serializer for Artwork
    """
    artist = serializers.CharField(source='artist.username', read_only=True)
    titles = TitleSerializer(many=True)
    emotions = serializers.SerializerMethodField()

    class Meta:
        model = Artwork
        fields = ('id', 'file', 'artist', 'index', 'url', 'titles', 'emotions')
        read_only_fields = ('id', 'artist', 'index', 'url', 'titles', 'emotions')

my title serializer:

class TitleSerializer(serializers.ModelSerializer):
    """
    Serializer for title suggested by user
    """
    votes = VoteSerializer(many=True, read_only=True)
    user = serializers.CharField(source='user.username', read_only=True)
   artwork = serializers.CharField(source='artwork.url', read_only=True)

    class Meta:
        model = Title
        fields = ('id', 'artwork', 'text', 'user', 'votes',)
        read_only_fields = ('id', 'artwork', 'user', 'votes',)

my artworks view:

class ArtworkView(viewsets.ModelViewSet):
    """
    View that handle Artwork
    """
    lookup_field = 'url'
    queryset = Artwork.objects.all()
    permission_classes = (
        permissions.IsAuthenticatedOrReadOnly,
        IsArtistOrReadOnly,
    )

    def get_serializer_class(self):
        if self.action == 'retrieve':
            return ArtworkDetailSerializer
        return ArtworkSerializer

Answer 1

When you order by the related field votes , this causes Django to do a left outer join. If a title is related to multiple votes, it is returned in the queryset once for each vote.

Note that saving the votes is not creating duplicates . You can confirm this by ordering by a different field, and checking the count. As you say in your question, the primary key of the duplicates is the same, so you have not created extra titles in the database, the queryset is just returning the same titles multiple times.

Title.objects.order_by('pk').count()

To order by the number of votes, you need to annotate the queryset with the number of votes, then order by the annotation:

Title.objects.annotate(num_votes=Count('votes')).order_by('num_votes')

Answer 2

You can try to replace:

vote = Vote.objects.create(title=title, user=user)

to

vote, created = Vote.objects.get_or_create(title=title, user=user)

Answer 3

the probleme was coming from my title models :

class Title(GenericModel):
    """
    Model for title suggested by user
    """
    class Meta:
        ordering = ['votes']

    text = models.CharField(_('text'), max_length=255)

    artwork = models.ForeignKey(Artwork, blank=True,    related_name='titles')

    user = models.ForeignKey(ArtLover, blank=True)

    def __str__(self):
        return self.text

the ordering in meta was duplicating the model everytime i vote why is this happening? and how im suppose to order my title by the number of vote they get ?