error-handling - 成功执行mysql查询时如何使用 'try catch finally' block 显示消息

Question

我一直在C#Windows表单的代码中使用“try catch finally”来查询MySQL数据库。该代码运行良好:当catch块标记错误时，将在消息框中显示错误消息。

在最后一块中，我编写了一个消息框，该框将显示成功更新数据库的时间。

如果没有错误消息，则一切正常。显示成功消息。

但是，如果有错误，则会在catch块中显示错误消息，然后在finally块中显示成功消息。

有谁知道解决方案，使程序在mysql更新时显示错误消息或成功消息？

谢谢，

彼得

这是一个代码示例:

private void btnUpdateEmployeeTable_Click(object sender，EventArgs e)//更新Employee表中的记录
{
字符串myConnection = @“server = localhost;数据库= shopdb;用户名= **;密码= ** ;转换为零datetime = True”;
MySqlConnection Connect = null;

        try
        {
            Connect = new MySqlConnection(myConnection);
            Connect.Open(); //Open the connection

            //This is the mysql command that we will query into the db.
            //It uses Prepared statements and the Placeholders for faster, more secure processing.

            String updateQuery = "UPDATE employee SET emp_lName = @empLastName, emp_fName = @empFirstName WHERE emp_number = @empNum";

            MySqlCommand cmdInsertEmployeeToDataBase = new MySqlCommand(updateQuery, Connect);
            cmdInsertEmployeeToDataBase.Prepare();

            //Bind the value to the placeholder               

            cmdInsertEmployeeToDataBase.Parameters.AddWithValue("@empNum", this.txtEmployeeNo.Text);
            cmdInsertEmployeeToDataBase.Parameters.AddWithValue("@empLastName", this.txtEmployeeLastName.Text);
            cmdInsertEmployeeToDataBase.Parameters.AddWithValue("@empFirstName", this.txtEmployeeFirstName.Text);                

            cmdInsertEmployeeToDataBase.ExecuteNonQuery(); //Execute the mysql command 


        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message + "\nDatabase could not be updated \n" + "Please try again");

        }
        finally
        {
            if (Connect != null)
            {
                Connect.Close(); //Close the connection
            }


            MessageBox.Show("Database update successful");


        }
    }

Answer 1

您可以轻松地将成功代码上移。如果在MessageBox.Show("Database update successful");行之前引发了异常，则它将永远不会执行。

     try
     {
        Connect = new MySqlConnection(myConnection);
        Connect.Open(); //Open the connection

        //This is the mysql command that we will query into the db.
        //It uses Prepared statements and the Placeholders for faster, more secure processing.

        String updateQuery = "UPDATE employee SET emp_lName = @empLastName, emp_fName = @empFirstName WHERE emp_number = @empNum";

        MySqlCommand cmdInsertEmployeeToDataBase = new MySqlCommand(updateQuery, Connect);
        cmdInsertEmployeeToDataBase.Prepare();

        //Bind the value to the placeholder               

        cmdInsertEmployeeToDataBase.Parameters.AddWithValue("@empNum", this.txtEmployeeNo.Text);
        cmdInsertEmployeeToDataBase.Parameters.AddWithValue("@empLastName", this.txtEmployeeLastName.Text);
        cmdInsertEmployeeToDataBase.Parameters.AddWithValue("@empFirstName", this.txtEmployeeFirstName.Text);

        cmdInsertEmployeeToDataBase.ExecuteNonQuery(); //Execute the mysql command 

        MessageBox.Show("Database update successful");

     }
     catch (Exception ex)
     {
        MessageBox.Show(ex.Message + "\nDatabase could not be updated \n" + "Please try again");

     }
     finally
     {
        if (Connect != null)
        {
           Connect.Close(); //Close the connection
        }

     }