如何使用 C# 将此 SQL 查询转换为 Linq

Question

由于我是 Linq 的新手，因此无法将此 SQL 查询转换为 Linq，因此我粘贴了我已经尝试过的代码，它给出了空记录。

提前致谢。

这是我尝试过的 Linq C# 语句：

from ts in Db.Tasks

join prt in Db.ProjectTasks on ts.Id equals prt.TaskId into PojTsk
from t1 in PojTsk 

join TL in Db.Timeline on ts.Id equals TL.TypeId into Tmln
from t2 in Tmln

join DUR in Db.Duration on ts.Id equals DUR.TypeId into Dur
from t3 in Tmln

where t1.ProjectId == ProjectId 
&& t2.Type == (int)Provider.EntityType.TASK 
&& t3.Type == (int)Provider.EntityType.TASK
select ts

这是我尝试使用 C# 转换为 Linq 的 SQL 查询：

SELECT 
    CONCAT('T', R1.Id)  as Id, 
    R1.Name, R1.Description, R1.Priority, 
    R1.Stage, R1.Status, R1.CreatorId, 
    R2.ProjectId, R3.StartDate, R3.EndDate, 
    R3.LatestEndDate, R3.LatestStartDate, 
    R3.EarliestStartDate, R3.ActualStart, R3.ActualEnd, 
    R3.RemTime, R3.ReshowDate, R3.RemTime, R3.Completed, 
    R4.ActualDuration, R4.ActualDurationPlanned      
FROM 
    (SELECT * 
     FROM [ProjectManagement].[dbo].[Tasks] AS TS) AS R1
JOIN
    (SELECT * 
     FROM [ProjectManagement].[dbo].[ProjectTasks]) AS R2 ON R1.Id = R2.TaskId
LEFT JOIN
    (SELECT * FROM [ProjectManagement].[dbo].[Timelines] 
     WHERE Type = 3) AS R3 ON R1.Id = R3.TypeId
LEFT JOIN
    (SELECT * FROM [ProjectManagement].[dbo].[Durations] 
     WHERE Type = 3) AS R4 ON R1.Id = R4.TypeId
WHERE
    ProjectId = 1

My sql query result in SQL Server Management Studio

Answer 1

即使仍然无法确定应该先执行哪个查询，我已经弄清楚了查询执行步骤：

(1) ProjectId = 1 的 ProjectTasks 表的内连接 Tasks 表，

(2) 左连接 (1) 到 Timelines 表，其中 Type = 3，

(3) 左连接 (2) 到类型 = 3 的持续时间表。

我最接近使用 LINQ 的 SQL 查询的方法（我既没有测试过 LINQPad，也没有直接测试过 VS）：

// first inner join
var query = (from R1 in Tasks
join R2 in ProjectTasks on R1.Id equals R2.TaskId into Group1

// second left join
from T1 in Group1.DefaultIfEmpty() 
join R3 in (from t in Timelines where t.Type == 3 select t) on T1.Id equals R3.TypeId into Group2

// third left join
from T2 in Group2.DefaultIfEmpty()
join R4 in (from d in Durations where d.Type == 3 select d) on T2.Id equals R4.TypeId

// still not sure to determine where condition here...
where T2.ProjectId == 1 // join result condition

select new {
    Id = T1.Id.ToString().Concat("T"), // assume Tasks.Id is an int identity column converted to String value
    Name = T1.Name,
    Description = T1.Description,
    Priority = T1.Priority,
    Stage = T1.Stage,
    Status = T1.Status,
    CreatorId = T1.CreatorId,
    ProjectId = T1.ProjectId,
    StartDate = T2.StartDate,
    EndDate = T2.EndDate,
    LatestEndDate = T2.LatestEndDate,
    EarliestStartDate = T2.EarliestStartDate,
    ActualStart = T2.ActualStart,
    ActualEnd = T2.ActualEnd,
    RemTime = T2.RemTime,
    ReshowDate = T2.ReshowDate,
    Completed = T2.Completed,
    ActualDuration = R4.ActualDuration,
    ActualDurationPlanned = R4.ActualDurationPlanned
}).ToList();

CMIIW。

Answer 2

试试这个：

from ts  in Db.Tasks
join prt in Db.ProjectTasks on ts.Id equals prt.TaskId
from tl  in Db.Timeline.Where(x => (x.TypeId == ts.Id)
                                && (x.Type == (int)Provider.EntityType.TASK))
                       .DefaultIfEmpty()
from dur in Db.Duration.Where(x => (x.TypeId == ts.Id)
                                && (x.Type == (int)Provider.EntityType.TASK))
                       .DefaultIfEmpty()

where  (prt.ProjectId == ProjectId)

select new {
    Id = "T" + ts.Id,
    ts.Name,
    ts.Description,
    //...

    prt.ProjectId,

    tl.StartDate,
    tl.EndDate,
    tl.LatestEndDate,
    //...

    dur.ActualDuration,
    dur.ActualDurationPlanned
}

from x in y.DefaultIfEmpty() 是一种创建LEFT JOIN 的简单方法。

编辑：在左连接中更改了.Where()。