Question

我需要计算一个对象拥有的子节点数，并通过对象序列化器在我的API中返回该值。我还需要计算这些子对象的子集。

我有一个带有孩子Asignees的Task对象。在我的API中，当我查询任务时，我希望返回以下数据集：

[
    { label: "Cross the bridge",
      count_assigned: 5,
      count_completed: 3 },
    { label: "Build a fire",
      count_assigned: 5,
      count_completed: 2 }
]

我该怎么做？我找到了.annotate()方法，但该结果在序列化程序类中不可用。

models.py

class Task(models.Model):
    label         = models.CharField(max_length=255,null=False,blank=False)

class Assignee(models.model):
    task         = models.ForeignKey(Task, related_name='assignees', on_delete=models.CASCADE, blank=True, null=True) 
    person       = models.ForeignKey(Person, on_delete=models.CASCADE, blank=True, null=True)
    completed    = models.DateTimeField(null=True,blank=True)

serializers.py

from rest_framework import serializers

from .models import Task, Assignee
from people.serializers import PersonSerializer

class AssigneeSerializer(serializers.ModelSerializer):
    id = serializers.ReadOnlyField()
    person = PersonSerializer(read_only=True)

    class Meta:
        model = Assignee

        fields = ('id','task','person','completed')
        read_only_fields = ['id']


class TaskSerializer(serializers.ModelSerializer):
    id = serializers.ReadOnlyField()

    class Meta:
        model = Task

        fields = ('id', 'label')
        read_only_fields = ['id']

Answer 1

建议的方式

            SqlConnection conn = connectLocaldb.ConnectDataBase();
        conn.Open();
        string sql = "INSERT INTO MemberCommitBeforeCompiling(Username,ProjectName,Version,GroupName,CommitTime,Branch) VALUES ('" + push.user_name + "','" + push.project.name + "','" + push.after + "','" + groupname + "',getdate(),'" + push.@ref + "') ";
        SqlCommand cmd = new SqlCommand(sql, conn);
        int result = cmd.ExecuteNonQuery();

http://www.django-rest-framework.org/api-guide/fields/#serializermethodfield

Answer 2

如果我理解你的逻辑，你可以尝试

在序列化程序中

class TaskSerializer(serializers.ModelSerializer):
    count_assigned = serializers.IntegerField(read_only=True)
    count_completed = serializers.IntegerField(read_only=True)

然后通过queryset：

from django.db.models import Count, Case, When, IntegerField

qs = Task.objects.annotate(
        count_completed=Count(Case(
            When(assignees__completed__isnull=False, then=1),
            output_field=IntegerField(),
        ))
    ).annotate(count_assigned=Count('assignees'))

serializer = TaskSerializer(qs, many=True)

模型中的效率非常低：

from django.utils.functional import cached_property

class Task(models.Model):

@cached_property
def all_assignee(self):
    return self.assignees.all()

def count_assigned(self):
    return self.all_assignee.count()

def count_completed(self):
    return self.all_assignee.filter(completed__isnull=False).count()

Django rest_framework：序列化程序

2 个答案: