Question

我不知道为什么我的连接一直关闭而没有任何关闭连接的东西。我已经尝试将它们封装在using块中，但无济于事。有没有更好的方法将单个选择查询传递到string？

private void button2_Click(object sender, EventArgs e)
{


    string username = txtUsername.Text;
    string password = txtPassword.Text;
    string query = "SELECT isActive FROM tblUser WHERE username = ?username AND password = ?password";

    MySqlCommand cmd = new MySqlCommand(query, con.connection);

    cmd.Parameters.AddWithValue("?username", username);
    cmd.Parameters.AddWithValue("?password", password);
    con.connection.Open();
    MySqlDataReader mdr = cmd.ExecuteReader();

    string isActive="";
    string updatequery = "UPDATE tbluser SET DateLastLogin= '" + DateTime.Today.ToString("dd-mm-yy") + "',TimeLastLogin = '" + DateTime.Now.TimeOfDay + "', IsActive = 1 WHERE username = ?username";
    if (mdr.HasRows)
    {
        if(con.connection.State == ConnectionState.Closed)con.connection.Open();
        while (mdr.Read())
        {
            isActive = mdr[0].ToString();
            if (isActive.Equals("1"))
            {
                MessageBox.Show("This user is already logged in!");
            }
            else
            {
                MySqlCommand updatecmd = new MySqlCommand(updatequery, con.connection);

                con.OpenConnection();
                updatecmd.Parameters.AddWithValue("?username", username);
                updatecmd.ExecuteNonQuery();
                pnlLogin.Hide();
                pnlMenu.Show();
                MessageBox.Show("Welcome " + username);

            }

        }

    }
    else
    {
        MessageBox.Show("Invalid user credentials.");
    }



}

Answer 1

由于您没有关闭连接（这是错误的），因此您无需验证您的con是否已关闭以打开它，因此您需要将其删除：

if(con.connection.State == ConnectionState.Closed)con.connection.Open();`

此外，您不需要再次打开您的连接，我相信正在关闭您的连接，因为您在con.OpenConnection();时使用!isActive.Equals("0")重新打开它。请尝试删除con.OpenConnection();并进行检查。

如果您在此代码之后的行后面没有任何新查询，则最好.Close()您的连接。

Answer 2

我为Update查询创建了第二个连接语句，并删除了打开连接的其他语句。

 private void button2_Click(object sender, EventArgs e)
    {


                string username = txtUsername.Text;
                string password = txtPassword.Text;
                string query = "SELECT isActive FROM tblUser WHERE username = ?username AND password = ?password";

                MySqlCommand cmd = new MySqlCommand(query, con.connection);

                    cmd.Parameters.AddWithValue("?username", username);
                    cmd.Parameters.AddWithValue("?password", password);
                    con.connection.Open();
                    MySqlDataReader mdr = cmd.ExecuteReader();

                    string isActive="";
                    string updatequery = "UPDATE tbluser SET DateLastLogin= '" + DateTime.Today.ToString("dd-mm-yy") + "',TimeLastLogin = '" + DateTime.Now.TimeOfDay + "', IsActive = 1 WHERE username = ?username";
                    if (mdr.HasRows)
                    {

                        while (mdr.Read())
                        {
                            isActive = mdr[0].ToString();
                            if (isActive.Equals("1"))
                            {
                                MessageBox.Show("This user is already logged in!");
                            }
                            else
                            {
                                MySqlCommand updatecmd = new MySqlCommand(updatequery, con.connection2);

                                con.connection2.Open();
                                    updatecmd.Parameters.AddWithValue("?username", username);
                                    updatecmd.ExecuteNonQuery();
                                    pnlLogin.Hide();
                                    pnlMenu.Show();
                                    MessageBox.Show("Welcome " + username);

                            }

                        }

                    }
                    else
                    {
                        MessageBox.Show("Invalid user credentials.");
                    }

                    con.CloseConnection();

    }

连接已关闭mysqldatareader

2 个答案: