SQL 转换为 LINQ 到实体答案

【问题标题】：SQL convert to LINQ to EntitiesSQL 转换为 LINQ 到实体
【发布时间】：2013-05-03 12:53:57
【问题描述】：

如何将此 SQL 语句转换为 LINQ to Entities。我找不到用 WHERE 子句合并表的方法

SQL：

Declare @DID int, @key varchar(50)

SET @DID = 3
SET @key = ''

SELECT TBL.GID, TBL.GName, TBL.DID FROM     
(
  SELECT TOP 1 (@DID*10000) AS [GID], '' AS [GName], @DID AS [DID] 
  FROM dbo.Employees E
  WHERE E.DepartmentID=@DID 
  AND (E.GroupID IS NULL OR E.GroupID = 0)  
  UNION ALL  
  SELECT G.GroupID AS [GID], G.GroupName AS [GName], G.DepartmentID AS [DID] 
  FROM dbo.Groups G
) TBL 
WHERE TBL.DID IN (@DID) 
AND TBL.GName IN 
(
  SELECT (CASE WHEN E.GroupID = 0 or E.GroupID IS NULL THEN '' 
          ELSE (SELECT G.GroupName FROM Groups G WHERE G.GroupID=E.GroupID) END) 
  FROM Employees E 
  WHERE E.DepartmentID = @DID 
  AND (E.FirstName + ' ' + E.LastName) LIKE '%' + @key + '%'
) 
ORDER BY TBL.GName DESC

LINQ to Entites：

var Details = (from a in Context.Employees
               where a.DepartmentID == DepartmentID
               && (a.GroupID == null || a.GroupID == 0)

               select new
               {
                 GID = Convert.ToInt32(DepartmentID * 10000),
                 GName = "",
                 DID = a.DepartmentID
               }

               ).Concat(
                 from a in Context.Groups
                 select new
                 {
                   GID = a.GroupID,
                   GName = a.GroupName,
                   DID = DepartmentID
                 }
               );

【问题讨论】：

标签： c# sql linq sql-server-2008 linq-to-entities

【解决方案1】：

每个查询的结果中创建的匿名类型是不同的类型，所以你不能Concat()他们。你可以像这样定义一个通用的Group 类...

class Group
{
  public int ID { get; set; }
  public int DepartmentID { get; set; }
  public string Name { get; set; }
}

然后拉出子查询并将结果创建为上述类的实例...

int deptID = 99;
string key = "foo";

var r1 = (from a in Context.Employees
          where a.DepartmentID == deptID
          && (!a.GroupID.HasValue || a.GroupID == 0)
          select new Group()
          {
            ID = a.DepartmentID * 10000,
            Name = string.Empty,
            DepartmentID = a.DepartmentID
          }
         ).Take(1);

var r2 = (from a in Context.Groups
          where a.DepartmentID == deptID
          select new Group()
          {
            ID = a.GroupID,
            Name = a.GroupName,
            DepartmentID = a.DepartmentID
          }
         );

var results = r1.Concat(r2); // UNION ALL the above 2 sets of results

然后创建过滤器集，最后用它过滤上面的结果...

var filter = (from e in Context.Employees
              join g in Context.Groups on g.GroupID equals e.GroupID into eg
              from subgrp in eg.DefaultIfEmpty()
              where e.DepartmentID == deptID
              && (e.FirstName + " " + e.LastName).Contains(key)
              select e.GroupID.HasValue && e.GroupID != 0 ? subgrp.GroupName : string.Empty 
             ).Distinct().ToList();

results = from a in results
          where filter.Contains(a.Name)
          orderby a.Name descending
          select a;

如果不完全符合您的需要，请随时发表评论。

【讨论】：