如何在 DRF 中通过单个 db 调用在多个父序列化器变量中使用单个嵌套序列化器的数据？答案

【问题标题】：How to use single nested serializer's data in more than one variable of parent serializer with single db call in DRF?如何在 DRF 中通过单个 db 调用在多个父序列化器变量中使用单个嵌套序列化器的数据？
【发布时间】：2022-01-06 09:51:16
【问题描述】：

如何在某处获取或存储 EmployeeSerializer 的数据，以便我可以再次使用它来获取活跃成员数，而不是调用新的数据库来获取活跃成员数？

class ProjectSerailizer(serializers.ModelSerializer):
  members = EmployeeSerializer(many=True)#returns all members of a project
  active_members_count = serializers.SerializerMethodField()# get count of members which are having status active
  class Meta:
    model = Project
    fields = ('id','name','members','active_members_count')
  
  def get_active_members_count(self,obj):
    #How can I omit this extra db call? as i am already having data in members variable from EmployeeSerializer, can i loop over members variable somehow and count the active ones?
    count = obj.members.filter(status='Active').count()
    return count

【问题讨论】：

标签： python django rest django-rest-framework django-serializer

【解决方案1】：

您可以使用select_related() 和过滤annotate() 在您的视图中设置查询集

django.db.models import Count, Q

queryset = Project.objects.select_related('members').annotate(
    active_members_count = Count('members', filter=Q(members__status = 'Active'))
)

然后您将在ProjectSerailizer 中获得active_members_count 和其他members 字段，而无需额外的数据库调用

【讨论】：