C#递归查询

一、sql

--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)

二、实现

//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\tName\tParent");
     query.ToList().ForEach(q=>Console.WriteLine("{0}\t{1}\t{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)));
}

或者：

        public static List<db_userinfo> findallchildren(int parentid)
        {
            var list = (from c in ctdt.db_userinfo
                        where c.parent_id == parentid
                        select c).ToList();
            List<db_userinfo> tmpList = new List<db_userinfo>(list);
            foreach (db_userinfo single in temp)
            {
                List<db_userinfo> tmpChildren = findallchildren(single.user_id);
                if (single.PB_Level == 1)//如果循环到最后一层退出
                {
                    return list;
                }
                if (tmpChildren.Count != 0)
                {
                    list.AddRange(tmpChildren);
                }
            }
            return list;
        }

转自：http://blog.csdn.net/q107770540/article/details/7708418和http://www.cnblogs.com/zhouhongyu1989/p/3796177.html感谢！