Django Queryset 获取特定类型的日期列表，使用 Postgres 数据库的唯一外键 id答案

【问题标题】：Django Queryset get list for the day of a particular type, unique foreignkey id using Postgres databaseDjango Queryset 获取特定类型的日期列表，使用 Postgres 数据库的唯一外键 id
【发布时间】：2018-05-23 11:37:08
【问题描述】：

我正在尝试查找查询以获取特定日期的最新出勤列表，其中包含已签到的唯一员工 (CHECKIN = 1)

下面是我的模型、记录和我想要完成的任务。

我的模型有 2 个模型：

class Employee(models.Model):
    fullname = models.CharField(max_length=30, blank=False)    

class Attendance(models.Model):
    CHECKIN = 1
    CHECKOUT = 2
    ATTENDANCE_TYPE_CHOICES = (
        (CHECKIN, "Check In"),
        (CHECKOUT, "Check Out"),
    )
    employee = models.ForeignKey(Employee)
    activity_type = models.IntegerField(choices = ATTENDANCE_TYPE_CHOICES, default=CHECKIN)
    timestamp = models.DateTimeField(auto_now_add=True)

假设我有以下记录：

Employee
{"id":1, "employee":"michael jackson",
"id":2, "fullname":"mariah carey",
"id":3, "fullname":"taylor swift"}

Attendance
{"id":1, "employee": 1,"activity_type": 1, timestamp: "2017-12-05 09:08", -interested in this for the activity type (1 for CHECKIN) and the date 2017-12-05, last of that employee id for that day
"id":2, "employee": 2,"activity_type": 1, timestamp: "2017-12-05 10:13",
"id":3, "employee": 3,"activity_type": 1, timestamp: "2017-12-05 11:30",
"id":4, "employee": 2,"activity_type": 2, timestamp: "2017-12-05 15:13", 
"id":5, "employee": 3,"activity_type": 2, timestamp: "2017-12-05 18:30", 
"id":6, "employee": 2,"activity_type": 1, timestamp: "2017-12-05 19:13", -interested in this for the activity type (1 for CHECKIN) and the date 2017-12-05, last of that employee id for that day
"id":7, "employee": 3,"activity_type": 1, timestamp: "2017-12-05 20:30", -interested in this for the activity type (1 for CHECKIN) and the date 2017-12-05, last of that employee id for that day
"id":8, "employee": 1,"activity_type": 2, timestamp: "2017-12-06 08:08"}

我很感兴趣，因此它仅根据 CHECKIN 的活动类型 1 和日期 2017-12-05 输出这 2 条记录，并且员工 ID 必须是唯一且最新的：

{"id":1, "employee": 1,"activity_type": 1, timestamp: "2017-12-05 09:08",
"id":6, "employee": 2,"activity_type": 1, timestamp: "2017-12-05 19:13"
"id":7, "employee": 3,"activity_type": 1, timestamp: "2017-12-05 20:30"}

我正在使用 Postgres 9.4

如何使用 Django 查询集产生预期的结果？

【问题讨论】：

标签： python django postgresql distinct django-queryset

【解决方案1】：

按activity_type过滤出勤率，按employee_id和-timestamp排序，然后在employee_id上使用distinct

Attendance.objects.filter(activity_type=Attendance.CHECKIN).order_by('employee_id','-timestamp').distinct('employee_id')

【讨论】：