C#.net 产生ID的情况

Question

我想在生成一个前段为字母，中段为年份，后段为递增的数，这样的一个ID如：XT20120012
我想从服务器提取时间，不想从客户端提取,而且怎么排除多用户同时生成时的重复？还有一个问题就是怎么才能让这个ID在年份改变的时候重新从0001开始排序哪？请各位大神给段代码！！谢谢！本人菜鸟中的菜鸟，请各位大神写的细一点，麻烦了！！

Answer 1

public static string AutoID(string TableName, string FiledName)
        {
            string SqlString = "select Max(" + FiledName + ")  from  " + TableName + "";            
            string ReturnID = DateTime.Now.ToString("XTyyyy");
            using (SqlConnection connetion = new SqlConnection(connectionString))
            {
                connetion.Open();
                using (SqlCommand Command =new SqlCommand(SqlString,connetion))
                {                  
                    string str = Command.ExecuteScalar().ToString();
                    if (!string.IsNullOrEmpty(str))
                    {                        
                        if (str.Substring(0, 6) != ReturnID)
                        {
                            ReturnID += ReturnID + "0001";
                        }
                        else
                        {
                            str = str.Substring(str.Length - 4, 4);
                            lReturnID += (Convert.ToInt32(str) + 1).ToString("0000");
                        }
                    }
                    else
                    {
                        ReturnID += "0001";
                    }
                }                    
            }
            return ReturnID;
        }

Answer 2

这个改一下if (str.Substring(0, 6) != ReturnID)
                        {
                            ReturnID +=  "0001";
                        }

Answer 3

public static string AutoID(string TableName, string FiledName)
        {
            string SqlString = "select Max(" + FiledName + ")  from  " + TableName + "";            
            string ReturnID = DateTime.Now.ToString("XTyyyy");
            using (SqlConnection connetion = new SqlConnection(connectionString))
            {
                connetion.Open();
                using (SqlCommand Command =new SqlCommand(SqlString,connetion))
                {                  
                    string str = Command.ExecuteScalar().ToString();
                    if (!string.IsNullOrEmpty(str))
                    {                        
                        if (str.Substring(0, 6) != ReturnID)
                        {
                            ReturnID += "0001";
                        }
                        else
                        {
                            str = str.Substring(str.Length - 4, 4);
                            ReturnID += (Convert.ToInt32(str) + 1).ToString("0000");
                        }
                    }
                    else
                    {
                        ReturnID += "0001";
                    }
                }                    
            }
            return ReturnID;
        }