Question

我不是一个LINQ程序员，所以这让我感到困惑。我有两个表：首先是带有StartDate和EndDate的计划，加上ID;其次，具有InstanceDate和ScheduleID的ScheduleInstance表。对于Schedule.StartDate和Schedule.EndDate之间的每一天，我需要创建一个ScheduleInstance行 - 但是，仅提前24小时。由于在24小时内创建和删除计划，我必须每隔n分钟生成一个检查程序，以检查ScheduleID的ScheduleInstance是否存在于该24小时窗口内。

型号：

public class Schedule
{
    public int ID { get; set; }
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
}
public class ScheduleInstance
{
    public int ID { get; set; }
    public int ScheduleID { get; set; }
    public DateTime InstanceDate { get; set; }
}

LINQ的开头：

var skeds = from sked in context.Schedules
            join instance in context.ScheduleInstances
                on sked.ID equals instance.ScheduleID
            where ((sked.StartDate <= DateTime.Now) && (sked.EndDate >= DateTime.Now))
            select sked.ID;

（显然错了）

总而言之，我需要获取Schedule.ID列表，其中ScheduleInstance.InstanceDate中的ScheduleInstance在接下来的24小时内不存在。

非常感谢您的帮助。

更新

        DateTime tomorrow = DateTime.Now.AddDays(1);
        var skeds = from sked in context.Schedules
                    join instance in context.ScheduleInstances
                         on sked.ID equals instance.ScheduleID into g
                    where (sked.StartDate <= tomorrow) &&
                          (sked.EndDate >= tomorrow) &&
                           !g.Any()
                    select sked;

现在这样可以创建一个实例（在后续代码中，这里不相关），如果明天不存在。如果我将StartDate设置为Now + 2mins，那么在2分钟之后创建Schedule也是完美的。但是，如果我24小时推进时钟，我应该得到一大堆新实例。重申一下，如果现在是一个计划开始日期，结束日期是30天之后，那么我最终应该有31个实例，每个新实例都会提前24小时创建。

Answer 1

我相信这会解决问题

var today = DateTime.Now;
var nextDay = today.AddDays(1);
var scheds = from sched in context.Schedules                        
             join instance in context.ScheduleInstances
                on sched.ID equals instance.ScheduleID into schedInstances
             where (sched.StartDate >= today) && 
                   (sched.EndDate <= nextDay) &&
                   !schedInstances.Any()
             select sched.ID;

Answer 2

所以你想要在日程表的StartDate和明天之间每天少于一个实例的日程安排？以下是如何实现这一目标的粗略概念：

DateTime tomorrow = DateTime.Now.AddDays(1);
var skeds = from sked in context.Schedules
            join instance in context.ScheduleInstances
                 on sked.ID equals instance.ScheduleID into g
            let instances = g.Where(x => x.InstanceDate >= sked.StartDate &&
                                         x.InstanceDate <= tomorrow)
            where (sked.StartDate <= tomorrow) &&
                  (sked.EndDate >= tomorrow) &&
                  (instances.Count() < (tomorrow - sked.StartDate).Days)
            select sked;

Answer 3

试试这个:(未经测试）

var skeds = from sked in context.Schedules
            from instance in context.ScheduleInstances
            where (sked.ID == instance.ScheduleID) && ((sked.StartDate <= DateTime.Now) && sked.EndDate >= DateTime.Now))
            select sked.ID;

Answer 4

一方面我应该采用KISS原则。另一方面，我有三个查询而不是一个。但它有效！

        var instances = from inst in context.ScheduleInstances
                        where (inst.StartDateTime >= DateTime.Now)
                        && (inst.StartDateTime < tomorrow)
                        select inst;

        var skeds = from sked in context.Schedules
                    where (sked.StartDate <= DateTime.Now)
                    && (sked.EndDate >= tomorrow)
                    select sked;

        var none = from sked in skeds
                   join inst in instances
                   on sked.ID equals inst.ScheduleID
                   into tg
                   from tcheck in tg.DefaultIfEmpty()
                   where tcheck == null
                   select sked;

Linq没有离开右边的桌子

4 个答案: