Question

这是问题所在。我试图在connection.Open执行查询及其抛出和异常。奇怪的是，在同一个应用程序上，我正在执行“选择”查询，它工作正常。但是当我执行“更新”查询时，它会抛出此Unable连接到任何指定的MySQL主机错误。一直被困在这上面。有人可以找出我出错的地方。

 private void button1_Click(object sender, EventArgs e)
    {
        if (radioButton1.Checked)
        {
            timerEnabled = 1;
        }

        connection.Open();

        //update the settings to the database table 
        MySqlCommand command = connection.CreateCommand();
        command.CommandText = "update Admin_Settings set Difficulty='" + comboBox3.Text + "'," + "NoOfQuestions='" + comboBox4.Text + "'," + "NoOfChoices='" + comboBox5.Text + "'," +
            "Subject='" + comboBox8.Text + "'," + "Timer='" + comboBox2.Text + "," + "TimerEnabled=" + timerEnabled + "," + "TimerType='" + comboBox1.Text + "'";


        command.ExecuteNonQuery();

        MessageBox.Show("Settings updated");
    }

Answer 1

我建议你做以下事情：

private void button1_Click(object sender, EventArgs e)
        {
            using (System.Data.SqlClient.SqlConnection connection = new System.Data.SqlClient.SqlConnection(connString))
            {
                if (radioButton1.Checked)
                {
                    timerEnabled = 1;
                }

                connection.Open();

                //update the settings to the database table 
                MySqlCommand command = connection.CreateCommand();
                command.CommandText = "update Admin_Settings set Difficulty='" + comboBox3.Text + "'," + "NoOfQuestions='" + comboBox4.Text + "'," + "NoOfChoices='" + comboBox5.Text + "'," +
                    "Subject='" + comboBox8.Text + "'," + "Timer='" + comboBox2.Text + "," + "TimerEnabled=" + timerEnabled + "," + "TimerType='" + comboBox1.Text + "'";


                command.ExecuteNonQuery();

                MessageBox.Show("Settings updated");
            }
        }

我知道你在想自己，你应该保持联系以便于使用和等等等等，但根据我的经验，这是浪费精力。什么最终会发生你不想要或不需要的麻烦。您最终没有意识到您在其他地方打开了连接，并且您花费数小时来解决您不应该做的事情。打开你的连接，完成后关闭它。

如果你想拥有一个连接对象，那很好，但是使用使用模式以便每次都处理它，并且总是从你的连接开始。

注意：用yoru MySqlConnection对象替换我的连接！

Answer 2

正如迈克所说，你总是更好地使用“使用”块，因为它一旦停止使用块就会处理任何连接。我在下面使用了两个用于连接的块，而另一个用于命令对象。

试试这个

    private void button1_Click(object sender, EventArgs e)
    {
        using (SqlConnection connection = new SqlConnection(connString))
        {
            if (radioButton1.Checked)
            {
                timerEnabled = 1;
            }

           string queryString = "update Admin_Settings set Difficulty='" +      
            comboBox3.Text + "'," + "NoOfQuestions='" + comboBox4.Text + "'," + 
            "NoOfChoices='" + comboBox5.Text + "'," + "Subject='" + comboBox8.Text +  
           "'," + "Timer='" + comboBox2.Text + "," + "TimerEnabled=" + timerEnabled +  
              "," + "TimerType='" + comboBox1.Text + "'";

          using (SqlCommand command = new SqlCommand(queryString, connection))
          {
            //update the settings to the database table 


            command.Connection.Open();
            command.ExecuteNonQuery();
            command.Connection.Close();

            MessageBox.Show("Settings updated");
          }
        }
    }

无法连接到任何指定的MySQL主机

2 个答案: