C# Mysql 多重查询

Question

我正在尝试构建一个小的状态工具。我需要获得多个查询的结果(大约 4-5 个)。一般连接设置和“如何读取数据”已经完成，但我无法弄清楚另一个查询是如何执行的。

我在搜索它时发现的所有内容都是针对 SqlClient 的。我对此完全负担过重。

到目前为止，这是我的代码(请耐心等待，我是新手):

private void button1_Click(object sender, EventArgs e)
        {
            if(listView1.Items.Count > 1)
            {
                listView1.Items.Clear();
            }
            var listMember = new List<string>{};
            var listOnline = new List<string>{};

            // SQL PART //
            string connString = "Server=10*****;Port=3306;Database=e***;Uid=e***;password=********************;";
            MySqlConnection conn = new MySqlConnection(connString);
            MySqlCommand command = conn.CreateCommand();
            command.CommandText = "SELECT fullname,online FROM member WHERE active = '1' ORDER BY online DESC";
            try
            {
                conn.Open();
            }
            catch (Exception ex)
            {
                listView1.Items.Add("Error: " + ex);
            }
            MySqlDataReader reader = command.ExecuteReader();
            while(reader.Read())
            {
                listMember.Add(reader["fullname"].ToString());
                listOnline.Add(reader["online"].ToString());
            }
            conn.Close();
            // SQL ENDING //

            // SET ENTRIES TO LISTVIEW //
            int counter = 0;
            foreach(string member in listMember)
            {
                ListViewItem item = new ListViewItem(new[] { member, listOnline.ElementAt(counter) });
                item.ForeColor = Color.Green;
                listView1.Items.Add(item);

                counter++;
            }
        }

我不太确定设计/布局最终会是什么样子，所以我想将结果附加到 sql-part 中的列表，以便稍后处理列表中的数据。

我真的必须在 conn.Close() 之后设置一个完整的新连接吗？或者还有其他办法吗？我可以想象:5 个查询有自己的连接、尝试、捕获和 2 个循环……这将得到大约 100-200 行，只是为了从 5 个查询中获取结果。这么简单的事情，是不是有点过分了？

希望得到一些帮助。问候。

根据新评论我的最新代码:

顶部:

public partial class Form1 : Form
{
    public static string connString = "Server=10****;Port=3306;Database=e****;Uid=e****;password=****;";
    public Form1()
    {
        InitializeComponent();
        MySqlConnection conn = new MySqlConnection(connString); // Error gone!
    }

正文部分:

 public void QueryTwoFields(string s, List<string> S1, List<string> S2)
        {
            try
            {
                MySqlCommand cmd = conn.CreateCommand(); // ERROR: conn does not exist in the current context.
                cmd.CommandType = CommandType.Text;
                string command = s;
                cmd.CommandText = command;
                MySqlDataReader sqlreader = cmd.ExecuteReader();
                while (sqlreader.Read())
                {
                    S1.Add(sqlreader[0].ToString());
                    S2.Add(sqlreader[1].ToString());
                }
                sqlreader.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }

private void button1_Click(object sender, EventArgs e)
        {
            if(listView1.Items.Count > 1)
            {
                listView1.Items.Clear();
            }
            var listMember = new List<string>{};
            var listOnline = new List<string>{};

            using (conn) // ERROR: conn does not exist in the current context.
            {
            conn.Open();
            ///...1st Query
            QueryTwoFields("SELECT fullname,online FROM member WHERE active = '1' ORDER BY online DESC",listMember,listOnline);
            //...2nd query
            //QueryTwoFields("your new Select Statement", otherList, otherList); 
            }
        }

Answer 1

您不必在每次执行一个查询时都关闭连接，而不必关闭分配给该连接的 sqlreader。最后，当所有查询都已执行后，您将关闭连接。还可以考虑使用 using:

您还可以定义一个方法来执行您的查询，以使您的代码不重复:

    public  void QueryTwoFields(string s, List<string> S1, List<string> S2)    
///Select into List S1 and List S2 from  Database (2 fields)
              {
                  try
                  {             
                          MySqlCommand cmd = conn.CreateCommand();
                          cmd.CommandType = CommandType.Text;
                          string command = s;
                          cmd.CommandText = command;
                          MySqlDataReader sqlreader = cmd.ExecuteReader();
                          while (sqlreader.Read())
                          {
                              S1.Add(sqlreader[0].ToString());
                              S2.Add(sqlreader[1].ToString());            
                          }
                          sqlreader.Close();

                  }
                  catch (Exception ex)
                  {                          
                     MessageBox.Show(ex.ToString());            
                  }                                           
              }
private void button1_Click(object sender, EventArgs e)
        {
            if(listView1.Items.Count > 1)
            {
                listView1.Items.Clear();
            }
            var listMember = new List<string>{};
            var listOnline = new List<string>{};

            // SQL PART //

    using (conn)
    {
       conn.Open();
       ///...1st Query
       QueryTwoFields("SELECT fullname,online FROM member WHERE active = '1' ORDER BY online DESC",listmember,listonline)
        //...2nd query
        QueryTwoFields("your new Select Statement",myOtherList1,myOtherlist2)    
      ....
    }
}

编辑:请记住，您不能在按钮处理程序中定义 QueryTwoFields 方法。您必须在外部定义它(请参阅上面的代码)。还要在程序的开头定义您的连接数据:

    namespace MyProject
    {
        /// <summary>
        /// Defiine your connectionstring and connection
        /// </summary>
        /// 

        public partial class Form1 : Form
        {  public static string connString = "Server=10*****;Port=3306;Database=e***;Uid=e***;password=********************;";              
           MySqlConnection  conn = new MySqlConnection(connString);

.........