Django QuerySet/Manager 按年龄从生日开始过滤员工

Question

我是初学者。我想列出年龄> 25 岁的员工名单并计算员工的平均年龄。目前，我们需要从生日开始计算年龄（我不知道它^^） .请帮我创建关于它的示例 QuerySet/Manager。

谢谢大家:))

我的模特：

class Employee(models.Model):
""""Employee model"""

    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    birthday = models.DateField(max_length=8)

注意：不会获取所有员工并从结果中过滤。 (results = Employee.objects.all()) 并且不使用原始 SQL。

Answer 1

如果您正在寻找自定义管理器，这是一个建议。

import datetime
from django.db import models

# Create your models here.


class EmployeeManager(models.Manager):
    def get_queryset(self):
        return super(EmployeeManager, self).get_queryset()

    def get_queryset_age_greater_25(self):
        # The `iterator()` method ensures only a few rows are fetched from the database at a time, saving memory.
        ids = [obj.id for obj in self.get_queryset().iterator() if obj.find_age() > 25]
        return self.get_queryset().filter(id__in=ids)

    def get_avg(self):
        sum_, count = sum(
            map(lambda obj: obj.find_age(), self.get_queryset_age_greater_25().iterator())), self.get_queryset_age_greater_25().count()
        return sum_/count


class Employee(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    birthday = models.DateField(max_length=8)
    objects = EmployeeManager()

    def find_age(self):
        return datetime.date.today().year - self.birthday.year

然后使用

Employee.objects.get_queryset_age_greater_25() # to get employee objects having age greater than 25)
Employee.objects.get_avg() # to get avg age of employees having age greater than 25)

Answer 2

from datetime import date
from dateutil.relativedelta import relativedelta

qs = Employee.objects.filter(birthdate__gt=date.today() - relativedelta(years=+25))

预计25年+1天就够了。由于闰年，使用函数relativedelta，以在 2020 年 2 月 29 日不引发 ValueError 异常。