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我使用的是 EF5 Code First，我有一个标准Tree类型结构，它是一堆嵌套Folder的 s。有些文件夹Device里面有 s。我想要做的是能够选择一个文件夹并找到该文件夹​​及其子文件夹中的所有设备。

经过一番挖掘，我似乎需要使用通用表表达式来生成我需要的数据。不幸的是，我真的很难做到这一点。

public class Folder
{
    public virtual ICollection<Folder> Children { get; set; }
    public virtual ICollection<Device> Devices { get; set; }
}

public class Device
{
    public virtual ICollection<Folder> PresentInFolders { get; set; }
 }

我试图根据这篇 MSDN 文章GetDevicesForFolderRecursively上的工作添加一个功能。该查询不完整，因为在我的情况下不起作用，因为设备可以位于多个文件夹中，因此它有一个文件夹列表。folder.FolderId equals device.FolderID

public IQueryable<Device> GetDevicesForFolderRecursively(int folderID)
{
    return from folder in this.FlatFolders
            join device in this.Devices on folder.FolderId equals device.FolderID
            where folder.FolderId == folderID
            select device;
}

一旦解决了这个问题，我也不知道如何准确地构建 CTE。MSDN 文章创建的 CTE 看起来像这样，但我不知道如何根据我的需要对其进行修改，以及这将如何递归工作？

context.Database.ExecuteSqlCommand(@"CREATE VIEW [dbo].[ManagerEmployees]
AS
    WITH    cte ( ManagerEmployeeID, EmployeeID )
              AS ( SELECT   EmployeeID ,
                            EmployeeID
                   FROM     dbo.Employees
                   UNION ALL
                   SELECT   e.EmployeeID ,
                            cte.EmployeeID
                   FROM     cte
                            INNER JOIN dbo.Employees AS e ON e.ReportsToEmployeeID = cte.ManagerEmployeeID
                 )
    SELECT  ISNULL(EmployeeID, 0) AS ManagerEmployeeID ,
            ISNULL(ManagerEmployeeID, 0) AS EmployeeID
    FROM    cte");

更新

我已经设法使 CTE 查询达到这种状态，但仍然无法正常工作。它不明白AS ( SELECT FolderId , [EstateManagerService].dbo.Devices.DeviceSerial，我不确定那里的价值是什么？

CREATE VIEW [dbo].[ManagerEmployees]
AS
WITH    cte ( FolderID, DeviceID )
          AS ( SELECT   FolderId ,
                        [EstateManagerService].dbo.Devices.DeviceSerial

               FROM     [EstateManagerService].dbo.Folders
               UNION ALL
               SELECT   e.Folder_FolderId,
                        cte.FolderID
               FROM     cte
                        INNER JOIN [EstateManagerService].dbo.FolderDevices AS e ON e.Folder_FolderId = cte.FolderID
             )
SELECT  ISNULL(DeviceID, 0) AS FolderID ,
        ISNULL(FolderID, 0) AS DeviceID
FROM    cte
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