在查询集中 Django DRF 中分别获取每个项目的计数

Question

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

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
            }
        ]
    }
]

这段代码为每个Department 提供了所有Employee count() 的输出：

期望的输出： 但我需要 3 个用于第一个部门，2 个用于第二个部门......

[
    {
        "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）。我尝试了以前的dep_count 定义（看上面的评论行。我留下它，因为它可能会帮助你帮助我）

Answer 1

如果您只想包含每个部门的员工人数，您可以替换它

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

类似这样的东西

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()