如何在 LINQ 中分组？

Question

我需要返回特定用户每日约会的最后 30 天，并检查该用户是否每天至少进行了 8 小时的约会。

在 sql 中我可以用这个命令做到这一点：

select IDAppointment,IDUser, SUM(DurationInHours) from Note where AppointmentDate > *lastmonth and IDUser = @userID group by IDUser,IDAppointment,AppointmentDate   

然后我得到结果并验证 DurationInHours(double 类型)。

是否可以使用 LINQ 来实现？ 获取上个月用户约会的列表并逐日验证

谢谢！

Answer 1

这应该是大致存在的，虽然这不在我的脑海中，因为不在 IDE 中。

var result = context.Notes
                    .Where(n => [Your where clause])
                    .GroupBy(n => new { n.IDUser, n.IDAppointment, n.AppointmentDate})
                    .Select(g => new {
                                   g.Key.IDAppointment,
                                   g.Key.IDUser,
                                   g.Sum(n => n.DurationInHours)});

更新：

作为参考，您的 where 子句将是这样的......（再次从我的脑海中浮出水面）

DateTime lastMonth = DateTime.Today.AddMonths(-1);
int userId = 1 // TODO: FIX
var result = context.Notes.Where(n => n.AppointmentDate > lastMonth
                                   && n.IDUser = userId)

导致....

DateTime lastMonth = DateTime.Today.AddMonths(-1);
int userId = 1 // TODO: FIX
var result = context.Notes
                    .Where(n => n.AppointmentDate > lastMonth
                             && n.IDUser = userId)
                    .GroupBy(n => new { n.IDUser, n.IDAppointment, n.AppointmentDate})
                    .Select(g => new {
                                   g.Key.IDAppointment,
                                   g.Key.IDUser,
                                   g.Sum(n => n.DurationInHours)});

Answer 2

这是我测试过的解决方案。

DateTime lastMonth = DateTime.Today.AddMonths(-1);
int selectedUserId = 2; 

var notes = new List<Note>(
    new Note[] {
        new Note() { 
            AppointmentDate = new DateTime(2013,7,30){}, 
            IDAppointment = 1, IDUser = 1, DurationInHours = 1
        },
        new Note() {
            AppointmentDate = new DateTime(2013,7,30){}, 
            IDAppointment = 1, IDUser = 1, DurationInHours = 2
        },
        new Note() {
            AppointmentDate = new DateTime(2013,7,30){}, 
            IDAppointment = 1, IDUser = 1, DurationInHours = 3
        },
        new Note() {
            AppointmentDate = new DateTime(2013,7,28){}, 
            IDAppointment = 2, IDUser =  2, DurationInHours = 2
        },
        new Note() {
            AppointmentDate = new DateTime(2013,7,28){}, 
            IDAppointment = 2, IDUser =  2, DurationInHours = 3
        },
        new Note() {
            AppointmentDate = new DateTime(2013,7,27){}, 
            IDAppointment = 2, IDUser =  2, DurationI nHours = 4
        },
        new Note() {
            AppointmentDate = new DateTime(2013,7,26){}, 
            IDAppointment = 3, IDUser =  3, DurationInHours = 3
        },
        new Note() {
            AppointmentDate = new DateTime(2013,7,25){}, 
            IDAppointment = 3, IDUser =  3, DurationInHours = 4
        },
        new Note() {
            AppointmentDate = new DateTime(2013,7,24){}, 
            IDAppointment = 3, IDUser =  3, DurationInHours = 5
        }
    }
);

var results = from n in notes
              group n by new {n.IDUser, n.IDAppointment, n.AppointmentDate}
              into g
              where g.Key.AppointmentDate > lastMonth && 
                    g.Key.IDUser == selectedUserId
              select new {
                  g.Key.IDAppointment, 
                  g.Key.IDUser, 
                  TotalHours = g.Sum(n => n.DurationInHours)
              };

需要明确地为 summation 属性指定一个名称（即 TotalHours），否则您会得到 错误 CS0746: Invalid anonymous type member declarator。必须使用成员分配、简单名称或成员访问来声明匿名类型成员。