從LINQ到SQL的SQL函數

Question

我想將以下sql過程更改為LINQ to SQL，任何人都可以幫助我。

http://vyaskn.tripod.com/hierarchies_in_sql_server_databases.htm

---

CREATE PROC dbo.ShowHierarchy (@Root int) AS
BEGIN
    SET NOCOUNT ON
    DECLARE @EmpID int, @EmpName varchar(30)

    SET @EmpName = (
        SELECT EmpName 
        FROM dbo.Emp 
        WHERE EmpID = @Root)

    PRINT REPLICATE('-', @@NESTLEVEL * 4) + @EmpName

    SET @EmpID = (
        SELECT MIN(EmpID) 
        FROM dbo.Emp 
        WHERE MgrID = @Root)

    WHILE @EmpID IS NOT NULL
    BEGIN
        EXEC dbo.ShowHierarchy @EmpID
        SET @EmpID = (
            SELECT MIN(EmpID) 
            FROM dbo.Emp 
            WHERE MgrID = @Root AND EmpID > @EmpID)
    END
END

Answer 1

在SQL Server中執行查詢的最有效方法是使用通用表表達式（簡稱CTE） 。 編寫一個存儲過程，並從Linq2Sql調用它。 除了Steven概述的方法（拔出雇主，然后遞歸調用該函數）會導致大量的數據庫查詢外，沒有一種真正有效的方法可以用純Linq做到。

Answer 2

嘗試這個：

public string[] ShowHierarchy(int employeeId)
{
    using (var db = new YourDataContext("yourConStr"))
    {
        return ShowHierarchyRecursive(db, employeeId, 1)
            .ToArray();
    }
}

private IEnumerable<string> ShowHierarchyRecursive(
    YourDataContext db, int employeeId, int level)
{
    // get the name of employeeId from db

    // yield return that name

    // get the list of people managed by that employeeId

    // foreach employee in that list,
    // call the ShowHierarchyRecursive, and
    // foreach item in the returned list yield return
    // that item.
}