使用 LINQ 获取连接表中的最大计数

Posted 2023-05-08

【中文标题】使用 LINQ 获取连接表中的最大计数

【英文标题】：Using LINQ to get Max Count in Junction Table

【发布时间】：2014-05-21 08:21:51

【问题描述】：

我在 *** 上遇到了很多问题，但恐怕我仍然找不到答案。我正在使用实体框架。使用 LINQ，我试图找到过去 7 天内最受欢迎的课程。我有四个表参与查询，Schedules、Sessions、Locations 和联结表ClientSessions

时间表的模型是

     public class Schedule
        public Guid ScheduleID  get; set; 
        public Guid CompanyID  get; set; 
        public Guid LocationID  get; set; 
        public Guid SessionID  get; set; 
        public Guid SessionTypeID  get; set; 
        public Guid ParentScheduleID  get; set; 
        public int ClassDay  get; set; 
        public int ClassMonth  get; set; 
        public int ClassYear  get; set; 
        public string Day  get; set; 
        public DateTime StartTime  get; set; 
        public DateTime EndTime  get; set; 
        public DateTime ClassDate  get; set;     
        public string Title  get; set; 
        public string Description  get; set; 
        public bool Deleted  get; set; 
        public int SessionSize  get; set;     
        public virtual Session Session  get; set; 
        public virtual Company Company  get; set; 
        public virtual Location Location  get; set; 
        public virtual SessionType SessionType  get; set; 
 

会话模型

 public class Session 

    public System.Guid SessionID  get; set; 
    public System.Guid ProgramID  get; set; 
    public System.Guid CompanyID  get; set; 
    public Nullable<Guid> SessionTypeID  get; set; 
    public Int32 SessionSize  get; set; 
    public bool Display  get; set; 
    public virtual ClientSession ClientSession  get; set; 

Junction ClientSession 表

    public class ClientSession

    public Guid ClientID  get; set; 
    public Guid CompanyID  get; set; 
    public Guid SessionID  get; set; 
    public Nullable<System.Guid> TransactionID  get; set;     
    // Navigation Properties
    public virtual Client Client  get; set; 
    public virtual Session Session  get; set; 

我编写了以下 SQL 代码，它按预期工作，但恐怕我没有足够的知识或经验将其转换为 Linq。

SELECT TOP 1 s.ClassDate, l.LocationName, COUNT(c.SessionID) as num_att 
FROM Schedules s 
JOIN Sessions ss ON s.SessionID = ss.SessionID
JOIN Sessions ss ON s.SessionID = ss.SessionID
JOIN ClientSessions c ON ss.SessionID = c.SessionID
JOIN Locations l ON s.LocationID = l.LocationID
WHERE s.CompanyID = '109'
AND s.LocationID = '4'
AND (s.ClassDate >= DATEADD(DAY, -7,  GETDATE()))
GROUP BY s.ClassDate, l.LocationName
ORDER BY num_att DESC, s.ClassDate DESC

这是我设法得到的

var details = _repositoryBase.AllIncluding<Schedule>(x => x.Session, x => x.Location)
.Where(x => x.CompanyID == mostPopularSessionRequest.CompanyID 
&& x.LocationID == mostPopularSessionRequest.LocationID
.GroupBy(x => x.ClassDate) 

如果能向我展示如何完成其​​余部分，我们将不胜感激。

提前感谢您的任何帮助。

【问题讨论】：

_repositoryBase.AllIncluding<Schedule>(x => x.Session, x => x.Location) 是否已经处理了 SQL 语句中的所有连接？

Hey Serv，是的，所有连接都在 AllIncluding 中处理。

这是一个存储库代码： public virtual IQueryable AllIncluding(params Expression>[] includeProperties) where TEntity : class IQueryable query = DataContext.Set(); foreach (var includeProperty in includeProperties) query = query.Include(includeProperty); 返回查询；

【参考方案1】：

 var query = from s in Schedules
                        join ss in Schedules on s.SessionID equals ss.SessionID
                        join c in ClientSessions on ss.SessionID equals c.SessionID
                        join l in Locations on s.LocationID equals l.LocationID
                        where s.CompanyID =  109  && s.LocationID = 4 && (s.ClassDate >= DateTime.Now.AddDays(-7))
                         group c by new
                        
                            c.ClassDate,
                            l.LocationName 
                         into gcs
                        select new  
                        
                            ClassDate = gcs.Key.ClassDate,
                            LocationName = gcs.Key.LocationName,
                            SessionIDCount = gcs.c.Count()
                        ;

【讨论】：

感谢 P John Raj。我会试一试，看看我会怎么走。我会告诉你。再次感谢您抽出宝贵时间回答。

我不得不重新调整连接以适应我的数据访问，但分组和选择工作完美。谢谢。

我注意到我身边的一个错误是我两次加入 Schedule