Django rest框架：嵌套序列化程序为空时排除结果

Question

我有一个可以工作的嵌套序列化程序，但我想排除嵌套序列化程序为空的实例。我在嵌套序列化程序上使用的过滤有效，但目前此代码返回所有站点，其中大多数在应用过滤器时具有空的 site_observations 数组。我只想返回包含 site_observations 的站点。我已经为 site_observations 尝试了 SerializerMethodField 但有同样的问题。使用 DRF 3.12

相关模型是站点，以及对站点有 FK 的观察，related field=site_observations

序列化器.py

class FilteredObsListSerializer(serializers.ListSerializer):
    def to_representation(self, data):
        projName = self.context["projName"]
    # this is my filter which works
        data = filter_site_observations(data, self.context["request"],
                                        projName)
        return super(FilteredObsListSerializer, self).to_representation(data)


class ObsFilterSerializer(serializers.ModelSerializer):
    class Meta:
        list_serializer_class = FilteredObsListSerializer
        model = Observation
        fields = "__all__"

class SiteSerializer(GeoFeatureModelSerializer):
    site_observations = ObsFilterSerializer(many=True)

    class Meta:
        model = Site
        geo_field = "geometry"
        fields = ("id", "name", "geometry", "site_observations")

views.py

class SiteList(generics.ListAPIView):
    queryset = Site.objects.all().order_by("pk")
    serializer_class = SiteSerializer
    
    # this is for filtering Observations on segment of an url:
    def get_serializer_context(self):
        context = super(SiteList, self).get_serializer_context()
        context.update({"projName": self.kwargs["name"]}) 
        return context

如何排除 site_observations 为空列表的站点？谢谢。

Answer 1

一种方法是告诉您的视图仅适用于满足某些条件的某些对象：

class SiteList(generics.ListAPIView):
    queryset = Site.objects.filter(
        site_observations__isnull=False,
    ).distinct().order_by('pk')

这将告诉SiteList 仅适用于存在site_observation 关系的Site 对象。您需要在这里调用distinct，如this 所述。

Answer 2

感谢您的建议，这导致了答案。没有在序列化程序中运行 filter_site_observations 有效。我重新设计了过滤器以在视图中运行并得到我需要的结果。 （我在使用 SerializerMethodField 之前尝试过，但无法正确过滤它；嵌套序列化器似乎是更好的方法。）感谢您的建议！这是过滤器：

def filter_site_observations(queryset, request, projName):
    '''
    filters a collection on project, observer status
    '''
    if request.user.is_authenticated:
        authprojects = [
            item.project.name
            for item in ObserverStatus.objects.filter(observer=request.user.id)
        ]
        if projName in authprojects:
            return queryset.filter(site_observations__project__name=projName)
        else:
            return queryset.filter(
                site_observations__project__name=projName).filter(
                    site_observations__private=False)
    else:
        return queryset.filter(
            site_observations__project__name=projName).filter(
                site_observations__private=False)

和views.py：

class SiteList(generics.ListAPIView):
    serializer_class = SiteSerializer

    def get_serializer_class(self, *args, **kwargs):
        if self.request.method in ("POST", "PUT", "PATCH"):
            return SitePostSerializer
        return self.serializer_class

    def get_queryset(self):
        projName = self.kwargs["name"]
        queryset = Site.objects.all().order_by('pk')
        queryset = filter_site_observations(queryset, self.request, projName)
        queryset = queryset.filter(
            site_observations__isnull=False, ).distinct()
        queryset = self.get_serializer_class().setup_eager_loading(queryset)
        return queryset

8 月 28 日更新 实际上，为了获得我需要的过滤器，我必须在both Observation 序列化程序和 SiteList views.py 中运行几乎相同的过滤器。无论我对子数据使用 SerializerMethodField 还是简单的嵌套序列化程序，这都是正确的。否则，我会得到：1) 所有站点，包括没有任何观察的站点，或 2) 具有一些非私有观察但也显示所有私有观察的站点。

filters.py

from users.models import ObserverStatus


def filter_site_observations(queryset, request, projName):
    '''
    filters a collection on project, observer status; used in views.py.
    Both of these filters seem to be required to get proper filtering.
    '''
    queryset = queryset.filter(site_observations__project__name=projName)

    if request.user.is_authenticated:
        authprojects = [
            item.project.name
            for item in ObserverStatus.objects.filter(observer=request.user.id)
        ]
        if projName in authprojects:
            return queryset
        else:
            return queryset.filter(site_observations__private=False)
    else:
        return queryset.filter(site_observations__private=False)


def filter_observations(queryset, request, projName):
    '''
    filters observations in ObsSerializer on observer status
    '''
    if request.user.is_authenticated:
        authprojects = [
            item.project.name
            for item in ObserverStatus.objects.filter(observer=request.user.id)
        ]
        if projName in authprojects:
            return queryset
        else:
            return queryset.filter(private=False)
    else:
        return queryset.filter(private=False)

所以我过滤了两次，不知道为什么会这样。