python - 分别获取查询集中每个项目的计数 Django DRF

Question

我的目标是获取与每个部门相关的Employee数量。例如，在 1 部门工作 3 名员工，在 2 部门工作另外 2 名员工。我想出了如何获取所有 Employee.objects.values('department').annotate(emp_count_in_dep=Count('department')).order_by('department') 的所有 Employee 计数.

models.py:

class Department(models.Model):
    dep_name = models.CharField(max_length=100)

    def __str__(self):
        return self.dep_name


class Employee(models.Model):
    emp_name = models.CharField(max_length=100)
    department = models.ForeignKey(Department, on_delete=models.CASCADE)

    def __str__(self):
        return self.emp_name

views.py:

class DepartmentView(viewsets.ModelViewSet):

    queryset = Department.objects.all()
    serializer_class = DepartmentSerializer


class EmployeeView(viewsets.ModelViewSet):

    queryset = Employee.objects.all()
    serializer_class = EmployeeSerializer

serializers.py:

class DepartmentSerializer(serializers.ModelSerializer):
    class Meta:
        fields = ('dep_name', 'organization')
        model = Department

    def get_emp_count_for_dep(self, obj):
        emp_count_for_dep = Employee.objects.values('department').annotate(emp_count_in_dep=Count('department')).order_by('department')
        return emp_count_for_dep


class EmployeeSerializer(serializers.ModelSerializer):
    dep_count = serializers.SerializerMethodField()
    # emp_id = serializers.IntegerField(write_only=True)
    # emp_id = serializers.ReadOnlyField()
    emp_id = serializers.PrimaryKeyRelatedField(queryset=Employee.objects.all())

    class Meta:
        fields = ('emp_id', 'emp_name', 'department', 'dep_count')
        model = Employee

    def get_dep_count(self, obj, emp_id=emp_id):
        # dep_count = Department.objects.values('employee').get(pk=emp_id)
        dep_count = Department.objects.annotate(dep_count=Count('employee')).count()
        return dep_count

输出:

[
    {
        "dep_name": "second department",
        "emp_count_for_dep": [
            {
                "department": 1,
                "emp_count_in_dep": 3
            },
            {
                "department": 2,
                "emp_count_in_dep": 2
            }
        ]
    },
    {
        "dep_name": "first department",
        "emp_count_for_dep": [
            {
                "department": 1,
                "emp_count_in_dep": 3
            },
            {
                "department": 2,
                "emp_count_in_dep": 2
            }
        ]
    }
]

这段代码为我提供了每个部门的所有Employee count()的输出:

期望的输出:但我第一部门需要 3 个，第二部门需要 2 个...

[
    {
        "dep_name": "first department",
        "emp_count_for_dep": [
            {
                "department": 1,
                "emp_count_in_dep": 3
            }
        ]
    },
    {
        "dep_name": "second department",
        "emp_count_for_dep": [
            {
                "department": 2,
                "emp_count_in_dep": 2
            }
        ]
    }
]

如您所见，我尝试了不同的方法(使用 IntegerField 和 ReadOnlyField)，还尝试了 self.instance.pk = 因为我需要 pk，因为我认为这有助于解决问题。我希望重写 get_dep_count 可以帮助我 - 例如添加一些参数，即 pk(主键)。我尝试了之前的 dep_count 定义(请查看上面的注释行。我保留它，因为它也许可以帮助您帮助我)

Answer 1

如果您只想包含每个部门的员 worker 数，您可以替换此内容

class DepartmentSerializer(serializers.ModelSerializer):
    class Meta:
        fields = ('dep_name', 'organization')
        model = Department

    def get_emp_count_for_dep(self, obj):
        emp_count_for_dep = Employee.objects.values('department').annotate(emp_count_in_dep=Count('department')).order_by('department')
        return emp_count_for_dep

像这样的东西

class DepartmentSerializer(serializers.ModelSerializer):

    emp_count_for_dep = serializers.SerializerMethodField()

    class Meta:
        fields = ('dep_name', 'organization', 'emp_count_for_dep')
        model = Department

    def get_emp_count_for_dep(self, obj):
        return Employee.objects.filter(department=obj).count()