数据库连接

[不尽的物语]

想定义一个数据库类访问APP_DATA的dmf文件，但是当执行到select函数时，打开 conn.Open();
就错误了，所以请各位

private SqlConnection conn = null;
public Mysql(string mdbFileName)
{
string _path = "~\\App_Data\\" + mdbFileName;
string str_conn = " Data Source="
+ System.Web.HttpContext.Current.Server.MapPath(_path);
//string strConn = ConfigurationManager.ConnectionStrings["SqlConnectionString"].ConnectionString;


try {
conn = new SqlConnection(str_conn);
}
catch (Exception)
{

}
public SqlDataReader Select(string SelectString)
{
string strError = "";

if (conn == null)
{

conn = Sqlconn();
}

try
{
//若数据库连接的当前状态是关闭的，则打开连接
if (conn.State == ConnectionState.Closed)
{

conn.Open();
}

SqlCommand selectCommand = new SqlCommand(SelectString, conn);
SqlDataReader dr = selectCommand.ExecuteReader();
return dr;
}
catch (Exception e)
{
strError = "数据检索失败：" + e.Message;
return null;
}


}

[xdashewan]

连接字符串不对吗？错误信息是什么？

[不尽的物语]

返回的dr为空，所以应该是执行到数据库时，有错误，然后执行返回空指令