Question

我正在使用带有MySQL后端的C＃创建客户端 - 服务器应用程序。我试图弄清楚创建了哪些对象乘以用于mysql的连接。问题的根源是没有正确结束连接。

我正在寻找一些方法来检查Visual Studio内部/外部创建连接的所有对象。

从MySQL方面我看到所有连接，其中有多少来自哪个客户端，但在客户端网站上我不知道哪个对象/后台工作者正在进行连接。

Answer 1

从我读到的内容我认为您要确保您的应用程序只打开1个连接并确保连接正确关闭。

我正在使用一个类来连接数据库，该数据库只有一个select方法可以打开和关闭连接，这样做的好处就是你不需要单身，或者需要担心多个线程，因为什么时候选择方法执行连接自动关闭：

/// <summary>
/// class which controlls the database, 
/// </summary>
public class DBConnect
{
    private MySqlConnection connection;

    /// <summary>
    /// the constructor which starts to initialize the database.
    /// </summary>
    /// <param name="username"></param>
    /// <param name="password"></param>
    public DBConnect(string username, string password)
    {
        Initialize(username, password);
    }

    /// <summary>
    /// initiates connection string for the database.
    /// </summary>
    /// <param name="username"></param>
    /// <param name="password"></param>
    private void Initialize(string username, string password)
    {
        string server = "Localhost";

        string database = "";
        string connectionString;
        connectionString = "SERVER=" + server + ";" + "DATABASE=" +
        database + ";" + "UID=" + username + ";" + "PASSWORD=" + password + ";";

        connection = new MySqlConnection(connectionString);
    }


    /// <summary>
    /// opens the connection to the database
    /// </summary>
    /// <returns></returns>
    private bool OpenConnection()
    {
        try
        {
            connection.Open();
            return true;
        }
        catch (MySqlException ex)
        {
            //When handling errors, you can catch your application's response based 
            //on the error number.
            //The two most common error numbers when connecting are as follows:
            //1042: Cannot connect to server.
            //1045: Invalid user name and/or password.
            switch (ex.Number)
            {
                case 1042:
                    MessageBox.Show("MySqlException: cannot connect to the server");
                    break;

                //case 1045:
                //    MessageBox.Show("Invalid username/password, please try again");
                //    break;
            }
            MessageBox.Show(ex.Message + "\r\n" +
                ex.StackTrace);
            return false;
        }
        catch (InvalidOperationException ioe)
        {
            Console.WriteLine(ioe);
            MessageBox.Show("Er is al een connectie geopend");
            return false;
        }
    }

    /// <summary>
    /// closes the connection with the database
    /// </summary>
    /// <returns>true or false depending on the succes of closing the connection</returns>
    private bool CloseConnection()
    {
        try
        {
            connection.Close();
            return true;
        }
        catch (MySqlException ex)
        {
            Console.WriteLine(ex.Message);
            return false;
        }
    }

    /// <summary>
    /// generally used to get multpile rows of data from the datbase
    /// </summary>
    /// <param name="query">SQL statement</param>
    /// <returns></returns>
    public DataTable Select(MySqlCommand cmd)
    {
        //Open connection
        if (this.OpenConnection() == true)
        {
            //Create Command
            cmd.Connection = connection;

            //Read the data and store it in a DataTable
            DataTable dt = new DataTable();
            MySqlDataAdapter da = new MySqlDataAdapter(cmd);
            try
            {
                da.Fill(dt);
            }
            catch (MySqlException e)
            {
                MessageBox.Show("An exception has occured loading the data: \n" + e.Message);
                Console.WriteLine(e.Message);
            }

            //close Connection
            this.CloseConnection();

            //return list to be displayed
            return dt;
        }
        else
        {
            return null;
        }
    }
}

Answer 2

我正在使用此代码：

public DataSet MySQL_Select(string query)
        {
            MySql.Data.MySqlClient.MySqlConnection msqlConnection = null;
            msqlConnection = new MySql.Data.MySqlClient.MySqlConnection("server=" + MYSQL_SERVER + ";user id=" + MYSQL_login + ";Password=" + MYSQL_password + ";database=" + MYSQL_SCHEMAS + ";persist security info=False; Allow Zero Datetime=true ");
DataSet DS = new DataSet();
            try
             {
                MySqlDataAdapter mySqlDataAdapter = new MySqlDataAdapter(query, msqlConnection);
                mySqlDataAdapter.Fill(DS);
            }
            catch (Exception er)
            {
                MessageBox.Show(er.Message);
            }
            finally
            {
                msqlConnection.Close();
            }
            return (DS);
        }

我能改进吗？为了确保我总是关闭连接，因为从我所知道的最后声明做得恰到好处。

Answer 3

史蒂夫的评论中提到，用使用块包装;一旦它超出范围，这将关闭并处理连接对象。

using (IDbConnection conn = new MySql.Data.MySqlClient.MySqlConnection(...))
{
    using (IDbCommand cmd = new MySql.Data.MySqlClient.MySqlCommand("select ...", conn))
    {
        conn.Open();

        var reader = cmd.ExecuteReader()';
        // process reader, etc
    }
}

IDisposable 实施者应该在使用中 IDbConnection 不应该是全局变量，它们应该在范围内构造，使用和处理，或者作为参数传递给方法。

使用mysql调试c＃代码的正确方法

3 个答案: