LINQ TO SQL 实现无限递归查询

from:http://blog.csdn.net/q107770540/article/list

见论坛内有网友提问类似的问题已经不止一次了，

现总结一下，希望能给以后再碰到此类问题的朋友一些帮助 

--构造测试数据： 只作演示用
CREATE TABLE [dbo].[Tim_LinqTable](
[Id] int PRIMARY KEY IDENTITY(1,1) NOT NULL,
[Name] [varchar](50) NOT NULL,
[Parent] int NOT NULL,
)
GO

INSERT INTO [Tim_LinqTable]
SELECT 'A',0 UNION ALL
SELECT 'A1',1 UNION ALL
SELECT 'A2',1 UNION ALL
SELECT 'B1',2 UNION ALL
SELECT 'B2',3 UNION ALL
SELECT 'C1',4 UNION ALL
SELECT 'C2',4 UNION ALL
SELECT 'D1',5 UNION ALL
SELECT 'D2',5 UNION ALL
SELECT 'D3',5
GO

WITH temp
AS
(
SELECT * FROM [Tim_LinqTable]  WHERE Parent = 3
UNION ALL
SELECT m.* FROM [Tim_LinqTable]  AS m
INNER JOIN temp AS child ON m.Parent = child.Id
)
SELECT * FROM temp
GO

--查询 Parent=3 的所有子数据结果如下:
Id          Name                                               Parent
----------- -------------------------------------------------- -----------
5           B2                                                 3
8           D1                                                 5
9           D2                                                 5
10          D3                                                 5

(4 row(s) affected)

//好，下边来看看用C#怎么实现上边的SQL语句吧：
void Main()
{
     var query=GetSonID(3);
     Console.WriteLine("Id	Name	Parent");
     query.ToList().ForEach(q=>Console.WriteLine("{0}	{1}	{2}",q.Id,q.Name,q.Parent));
     /*
        Id       Name       Parent
        5        B2         3
        8        D1         5
        9        D2         5
            10        D3         5
     */
}
public IEnumerable<Tim_LinqTable> GetSonID(int p_id)
{
    var query = from c in this.Tim_LinqTables
           where c.Parent  == p_id
           select c;

    return  query.ToList().Concat(query.ToList().SelectMany(t => GetSonID(t.Id)));
}