Python Django中相关模型的有效计数

在我的Django应用程序中，当我将

host\u count

字段添加到序列化程序中以获取每个域的主机数时，API响应的性能会显著降低

• 无主机计数时：300ms
• 使用主机计数时：15秒

我尝试将“主机集”添加到与预回迁相关的方法中，但没有帮助

使用Count的注释在这里对我有帮助吗？如何优化此值的获取

序列化程序.py

class DomainSerializer(serializers.Serializer):
    name = serializers.CharField(read_only=True)
    org_name = serializers.CharField(source='org.name', read_only=True)
    created = serializers.DateTimeField(read_only=True)
    last_host_search = serializers.DateTimeField(read_only=True)
    host_count = serializers.SerializerMethodField()

    def get_host_count(self, obj):
        return Host.objects.filter(domain=obj).count()

class DomainList(generics.ListAPIView):
    def get(self, request, format=None):
        domains = Domain.objects.prefetch_related('org').all()
        serializer = DomainSerializer(domains, many=True)
        return Response(serializer.data)

class Domain(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    last_host_search = models.DateTimeField(auto_now=True)
    name = models.CharField(unique=True, max_length=settings.MAX_CHAR_COUNT, blank=False, null=False)
    org = models.ForeignKey(Org, on_delete=models.CASCADE, blank=True, null=True)

视图.py

class DomainSerializer(serializers.Serializer):
    name = serializers.CharField(read_only=True)
    org_name = serializers.CharField(source='org.name', read_only=True)
    created = serializers.DateTimeField(read_only=True)
    last_host_search = serializers.DateTimeField(read_only=True)
    host_count = serializers.SerializerMethodField()

    def get_host_count(self, obj):
        return Host.objects.filter(domain=obj).count()

class DomainList(generics.ListAPIView):
    def get(self, request, format=None):
        domains = Domain.objects.prefetch_related('org').all()
        serializer = DomainSerializer(domains, many=True)
        return Response(serializer.data)

class Domain(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    last_host_search = models.DateTimeField(auto_now=True)
    name = models.CharField(unique=True, max_length=settings.MAX_CHAR_COUNT, blank=False, null=False)
    org = models.ForeignKey(Org, on_delete=models.CASCADE, blank=True, null=True)

型号.py

class DomainSerializer(serializers.Serializer):
    name = serializers.CharField(read_only=True)
    org_name = serializers.CharField(source='org.name', read_only=True)
    created = serializers.DateTimeField(read_only=True)
    last_host_search = serializers.DateTimeField(read_only=True)
    host_count = serializers.SerializerMethodField()

    def get_host_count(self, obj):
        return Host.objects.filter(domain=obj).count()

class DomainList(generics.ListAPIView):
    def get(self, request, format=None):
        domains = Domain.objects.prefetch_related('org').all()
        serializer = DomainSerializer(domains, many=True)
        return Response(serializer.data)

class Domain(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    last_host_search = models.DateTimeField(auto_now=True)
    name = models.CharField(unique=True, max_length=settings.MAX_CHAR_COUNT, blank=False, null=False)
    org = models.ForeignKey(Org, on_delete=models.CASCADE, blank=True, null=True)

您可以使用统计同一查询中的相关对象：

from django.db.models import Count

class DomainList(generics.ListAPIView):
    def get(self, request, format=None):
        domains = Domain.objects.prefetch_related('org').annotate(
            host_count=Count('host')
        )
        serializer = DomainSerializer(domains, many=True)
        return Response(serializer.data)

从django.db.models导入计数
类DomainList（generics.ListAPIView）：
def get（自我、请求、格式=无）：
domains=Domain.objects.prefetch_related（'org'）。注释(
主机计数=计数（'主机'）
)
serializer=DomainSerializer（域，多个=True）
返回响应（serializer.data）

在序列化程序中，只需检索相应的属性：

class DomainSerializer(serializers.Serializer):
    name = serializers.CharField(read_only=True)
    org_name = serializers.CharField(source='org.name', read_only=True)
    created = serializers.DateTimeField(read_only=True)
    last_host_search = serializers.DateTimeField(read_only=True)
    host_count = serializers.IntegerField(read_only=True)

class DomainSerializer（serializers.Serializer）：
name=serializers.CharField（只读=True）
org\u name=serializers.CharField（source='org.name'，read\u only=True）
created=serializers.DateTimeField（只读=True）
last_host_search=serializers.DateTimeField（只读=True）
主机计数=序列化程序。整型字段（只读=真）

这将生成一个如下所示的查询：

SELECT domain.*, org.*, COUNT(host.id)
FROM domain
LEFT OUTER JOIN org ON domain.org_id = org.id
LEFT OUTER JOIN host ON host.domain_id = domain.id
GROUP BY domain.id, org.id

选择域。*、组织。*、计数（host.id）
来自域
domain.org_id=org.id上的左外部加入组织
host.domain_id=domain.id上的左外部联接主机
按domain.id、org.id分组

谢谢！这解决了我的问题。