Oracle.DataAccess.Client.OracleException C#

Question

在这个类中，我从数据库中选择两个值，并将其与用户提供的textbox值进行比较。下面是我的班。

     public void Userlogin(TextBox username, TextBox pwd)
    {
        int _failedAttempt = 0;

        OpenConnection();

        command = new OracleCommand();
        command.CommandText = "SELECT username, user_pwd FROM dinein_system_users WHERE username:usrname AND user_pwd:pwd";
        command.Connection = dbconnect;
        command.BindByName = true;

        try
        {
            command.Parameters.Add("usrname", username.Text);
            command.Parameters.Add("pwd", pwd.Text);
        }
        catch (NullReferenceException NRE)
        {
            MessageBox.Show("Please contact your developer about this error. Thank you " + NRE);
        }

        _reader = command.ExecuteReader();
        if (_reader.Read() != true)
        {
            _failedAttempt = _failedAttempt + 1;
            while (_failedAttempt < 3)
            {
                MessageBox.Show("Incorrect Username or Password. Please try again " + "Attempts: " + _failedAttempt);
                username.ResetText();
                pwd.ResetText();
            }
        }
        else
        {
            MessageBox.Show("Welcome");
        }
    }

我的连接字符串

this._connectionString = "Data Source=xe;Max Pool Size=50;Min Pool Size=1;Connection Lifetime=120;Enlist=true;User Id=hr;Password=hr";

所以当程序执行时，我会得到这个错误。

An unhandled exception of type 'Oracle.DataAccess.Client.OracleException' occurred in Oracle.DataAccess.dll

附加信息:外部组件引发异常。在过去的一小时里，我一直在此工作，任何帮助都将不胜感激。

更新

开放连接方法

public void OpenConnection()
    {
        try
        {
            if (dbconnect == null)
            {
                dbconnect = new OracleConnection(this._connectionString);
                dbconnect.Open();
                return;
            }

            switch (dbconnect.State)
            {
                case ConnectionState.Closed:
                case ConnectionState.Broken:
                    dbconnect.Close();
                    dbconnect.Dispose();
                    dbconnect = new OracleConnection(this._connectionString);
                    dbconnect.Open();
                    return;
            }
        }
        catch (OracleException oracleException)
        {
            MessageBox.Show("Database connectionString is null. Contact your developer! " + oracleException);
        }

    }

异常堆栈跟踪

   at Oracle.DataAccess.Client.OracleException.HandleErrorHelper(Int32 errCode, OracleConnection conn, IntPtr opsErrCtx, OpoSqlValCtx* pOpoSqlValCtx, Object src, String procedure, Boolean bCheck)
   at Oracle.DataAccess.Client.OracleException.HandleError(Int32 errCode, OracleConnection conn, String procedure, IntPtr opsErrCtx, OpoSqlValCtx* pOpoSqlValCtx, Object src, Boolean bCheck)
   at Oracle.DataAccess.Client.OracleCommand.ExecuteReader(Boolean requery, Boolean fillRequest, CommandBehavior behavior)
   at Oracle.DataAccess.Client.OracleCommand.ExecuteReader()
   at DINEIN.OracleDB_Connection.Userlogin(TextBox username, TextBox pwd) in f:\My Documents\Projects\DINEIN\DINEIN\OracleDB_Connection.cs:line 92
   at DINEIN.Login.btn_login_Click(Object sender, EventArgs e) in f:\My Documents\Projects\DINEIN\DINEIN\Login.cs:line 31
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.PerformClick()
   at System.Windows.Forms.Form.ProcessDialogKey(Keys keyData)
   at System.Windows.Forms.Control.ProcessDialogKey(Keys keyData)
   at System.Windows.Forms.Control.PreProcessMessage(Message& msg)
   at System.Windows.Forms.Control.PreProcessControlMessageInternal(Control target, Message& msg)
   at System.Windows.Forms.Application.ThreadContext.PreTranslateMessage(MSG& msg)
       at System.Windows.Forms.Application.ThreadContext.System.Windows.Forms.UnsafeNativeMethods.IMsoComponent.FPreTranslateMessage(MSG& msg)
   at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.Run(Form mainForm)
   at DINEIN.Program.Main() in f:\My Documents\Projects\DINEIN\DINEIN\Program.cs:line 19
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

Answer 1

与其使用单独的OpenConnection()方法，不如考虑使用using()语句进行编码。它将确保您的连接(一个与数据库相关的其他对象)总是被释放.

例如：

int _failedAttempt = 0;

public void Userlogin(TextBox username, TextBox pwd)
{
  try
  {
    using (var connection = new OracleConnection(_connectionString))
    {
      connection.Open();

      using (var command = new OracleCommand())
      {
        command.CommandText = "SELECT username, user_pwd FROM dinein_system_users WHERE username= :usrname AND user_pwd= :pwd";
        command.Connection = connection;
        command.BindByName = true;

        command.Parameters.Add("usrname", username.Text);
        command.Parameters.Add("pwd", pwd.Text);

        using (var reader = command.ExecuteReader())
        {
          if (reader.Read() != true)
          {
            _failedAttempt += 1;
            if (_failedAttempt < 3)
            {
              MessageBox.Show("Incorrect Username or Password. " +
                              "Please try again. " + 
                              $"Attempts: {_failedAttempt}");
              username.ResetText();
              pwd.ResetText();
            }
            else
            {
              // 3 failed attempts
            }
          }
          else
          {
            _failedAttempt = 0;
            MessageBox.Show("Welcome");
          }
        }
      }
    }
  }
  catch(OracleException ex)
  {
    MessageBox.Show("Error: {ex}");
  }
}