 
using System; 
using System.Data.OleDb; 
namespace ConsoleApplication1 
{ 
class Program 
{ 
static void Main(string[] args) 
{ 
Console.WriteLine(GetUserId("dnawo")); 
Console.ReadKey(); 
} 
/// <summary> 
/// 獲取用戶Id 
/// </summary> 
/// <param name="name"></param> 
/// <returns></returns> 
static int GetUserId(string name) 
{ 
using (OleDbConnection conn = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=F:\db1.mdb")) 
{ 
conn.Open(); 
using (OleDbCommand cmd = new OleDbCommand()) 
{ 
cmd.Connection = conn; 
cmd.CommandText = "select Id from UserTB where UserName='" + name + "'"; 
object val = cmd.ExecuteScalar(); 
if (val != null) 
return int.Parse(val.ToString()); 
else 
{ 
cmd.CommandText = string.Format("insert into UserTB(UserName) values('{0}')", name); 
cmd.ExecuteNonQuery(); 
return GetUserId(name); 
} 
} 
conn.Close(); 
} 
} 
} 
} 

經(jīng)測試，當用戶不存在時，執(zhí)行上邊代碼后Access表中總會新增兩條一樣的記錄：

改用SQL Server數(shù)據(jù)庫不會有上述問題，經(jīng)多次測試又發(fā)現(xiàn)，若在"return GetUserId(name);"處設(shè)置斷點，稍停一會也不會出現(xiàn)上述問題。最終代碼修改如下運行正常：

復制代碼代碼如下:

 
using System; 
using System.Data.OleDb; 
namespace ConsoleApplication1 
{ 
class Program 
{ 
static void Main(string[] args) 
{ 
Console.WriteLine(GetUserId("dnawo")); 
Console.ReadKey(); 
} 
/// <summary> 
/// 獲取用戶Id 
/// </summary> 
/// <param name="name"></param> 
/// <returns></returns> 
static int GetUserId(string name) 
{ 
int id = 0; 
using (OleDbConnection conn = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=F:\db1.mdb")) 
{ 
conn.Open(); 
using (OleDbCommand cmd = new OleDbCommand()) 
{ 
cmd.Connection = conn; 
cmd.CommandText = "select Id from UserTB where UserName='" + name + "'"; 
object val = cmd.ExecuteScalar(); 
if (val != null) 
id = int.Parse(val.ToString()); 
else 
{ 
cmd.CommandText = string.Format("insert into UserTB(UserName) values('{0}')", name); 
cmd.ExecuteNonQuery(); 
} 
} 
conn.Close(); 
} 
return id == 0 ? GetUserId(name) : id; 
} 
} 
} 