Linq左不在右表

Question

我不是一個LINQ程序員，所以這有點讓我感到困惑。我有兩個表格：第一個帶有StartDate和EndDate的Schedule，加上ID;其次，具有InstanceDate和ScheduleID的ScheduleInstance表。對於Schedule.StartDate和Schedule.EndDate之間的每一天，我都需要創建一個ScheduleInstance行 - 但是，只需要提前24小時。由於在24小時內預先創建並刪除了日程表，我必須每n分鐘產生一個檢查器，以檢查ScheduleID的ScheduleInstance是否存在於該24小時窗口內。

型號：

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; } 
} 

的LINQ的開始：

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; 

（顯然是錯誤的）

總之，我需要得到Schedule.ID的列表，其中一個ScheduleInstance對於ScheduleInstance.InstanceDate在接下來的24小時內不存在。

非常感謝您的幫助。

UPDATE

 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; 

這現在工作在一個實例被創建（在後面的代碼，這裏不相關），如果不爲明天存在。如果我將StartDate設置爲「現在+2分鐘」，那麼在2分鐘後，該計劃將被創建 - 完美。但是，如果我24小時提前，我應該會得到一大堆新實例。重申一下，如果現在計劃的開始日期是30天，並且結束日期是30天，那麼最終應該有31個實例，並且每個新實例都要提前24小時創建。

Answer 1

一方面，我應該採用吻原則。另一方面，我有三個查詢，而不是一個。但它的作品！

 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; 

Answer 2

我相信這將這樣的伎倆

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 3

試試這個：（未經測試）

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

所以，你要的是有計劃的開始日期和明天之間的每天不到一個實例時間表？這裏有一個大概的想法：

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;