Question

我想将以下查询（工作正常）从查询语法转换为LINQ语法，但我似乎无法做到正确：

SELECT
    [t1].[ID], [t1].[ParentID], [t1].[FolderName],
    [t1].[Purpose], [t1].[IsSystem],t1].IsHidden],
    [t1].[ChangeSrc], [t1].[SyncGUID], [t1].[CreationDBTimeStamp]
FROM [dbo].[FileStorageFolders] AS [t0]
INNER JOIN [dbo].[FileStorageFolders] AS [t1] ON ([t0].[ID]) = [t1][ParentID]
WHERE ([t1].[Purpose] = @p0)
    AND ([t1].[FolderName] = @p1)
    AND ([t0].[ParentID] IS NULL)
    AND ([t0].[Purpose] = @p2)

我使用此LINQ语法，但结果始终为null值：

 private static FileStorageFolder GetCapsuleContentFolder(FileStorageDataContext db)
    {    IQueryable<FileStorageFolder> source = (from dbfolder in db.FileStorageFolders
            join dbsubfolder in db.FileStorageFolders on
                new { ParentID = dbfolder.ID } equals
                new { ParentID = Convert.ToInt32(dbsubfolder.ParentID) }
            where
                dbfolder.ParentID == null &&
                dbfolder.Purpose == 'REPORT' &&
                dbsubfolder.Purpose == 'LayoutFolder' &&
                dbsubfolder.FolderName == 'LayoutReport'
            select new
                    {
                        dbsubfolder.ID,
                        ParentID = (System.Int32?)dbsubfolder.ParentID,
                        dbsubfolder.FolderName,
                        dbsubfolder.Purpose,
                        dbsubfolder.IsSystem,
                        pqrentID2 = dbfolder.ParentID,
                        Purpose2 = dbfolder.Purpose
                    }) as IQueryable<FileStorageFolder>;
return source.Single();
}

Answer 1

您是否在父母身上收集了儿童费用？如果您的关系已映射，则应该。在这种情况下，您可以尝试：

var query = from dbFolder in db.FileStorageFolders
            from subFolder in dbFolder.SubFolders // Here I use that mapped relations
            where ...
            select new { ... };

您的查询的问题是您正在创建匿名类型并将其转换为您的类型 - 这是不可能的。此外，它不是完整的分层查询（您的SQL不是很好）。它只会选择一个级别的子文件夹。

LINQ to SQL递归问题

1 个答案: