如何在 Django 多对多关系中计算包含特定值的项目

Question

我有一个用于注释的 django 应用程序，我通过多对多关系将有关图像注释的信息保存到模型 BiomarkerAnnotations 中。我使用annotated 字段跟踪哪些用户完成了图像注释。

from django.contrib.auth.models import User

class Biomarker(models.Model):   
    name = models.CharField(max_length=256)
    description = models.CharField(max_length=1024)

class Image(models.Model):
    number = models.IntegerField(default=0)
    absolute_path = models.CharField(max_length=2560)
    biomarkers = models.ManyToManyField(Biomarker, through='BiomarkerAnnotations', related_name="biomarker_annotations")
    annotated = models.ManyToManyField(User, related_name="annotated_by")

class BiomarkerAnnotations(models.Model):
    _image = models.ForeignKey(Image, on_delete=models.CASCADE)
    biomarker = models.ForeignKey(Biomarker, on_delete=models.CASCADE)
    user = models.ForeignKey(User, null=True,on_delete=models.SET_DEFAULT, default=1)     

我想创建一个视图，为特定用户（发送请求的用户）返回他已注释的图像数量以及还有多少图像需要注释。到目前为止，我已经达到了这一点，但它似乎不起作用：查询返回的总计数大于图像计数。

class AnnotStatsSerializer(serializers.ModelSerializer):
    annotations = serializers.IntegerField()
    count = serializers.IntegerField()

    class Meta:
        model = Image
        fields = ("count", "annotations")

class AnnotatedStatsViewSet(viewsets.ReadOnlyModelViewSet):
    queryset = Image.objects.all()
    serializer_class = AnnotStatsSerializer


    def get_queryset(self):
        queryset = self.queryset
        user_object = self.request.user

        project_id = self.request.query_params.get('project', None)
        if project_id is None: raise Http404

        queryset = queryset.annotate(annotations=Case(When(annotated__id__exact=user_object.id, then=Value(1)), default=Value(0), output_field=IntegerField())) \
                           .values('annotations').annotate(count=Count('annotations')).order_by('annotations') \
                           .values('count', 'annotations')

        return queryset

任何帮助表示赞赏。

Answer 1

您可以使用：

annotated_images = Image.objects.filter(
    biomarkerannotations__user=user_object
).count()
images_todo = Image.objects.exclude(
    biomarkerannotations__user=user_object
).count()

获取annotated_images和images_todo的数量。

或者如果您正在使用annotated 多对多关系：

annotated_images = Image.objects.filter(
    annotated=user_object
).count()
images_todo = Image.objects.exclude(
    annotated=user_object
).count()

我们可以让这组用户使用：

from django.db.models import Count, OuterRef, Subquery, Value

User.objects.annotate(
    tagged=Count('annotated_by'),
    not_tagged=Subquery(
        Image.objects.exclude(
            annotated=OuterRef('pk'),
        ).values(foo=Value(None)).values(
            total=Count('pk')
        ).order_by(Value(None))
    )
)

这会产生一个如下所示的查询：

SELECT auth_user.*,
       COUNT(app_name_image_annotated.image_id) AS tagged
       (
           SELECT COUNT(V0.id) AS total
           FROM app_name_image V0
           WHERE NOT EXISTS
               (
                   SELECT (1) AS a
                   FROM app_name_image_annotated U1
                   WHERE U1.user_id = auth_user.id AND U1.image_id = V0.id
                   LIMIT 1
               )
       ) AS not_tagged FROM auth_user
LEFT OUTER JOIN app_name_image_annotated ON (auth_user.id = app_name_image_annotated.user_id)
GROUP BY auth_user.*