c# - C# 结构中的 MySQL 错误

Question

我在程序中遇到 MySQL 问题。我对此并不专业。

错误消息:

"MySql.Data.MySqlClient.MySqlException: There is already an open DataReader associated with this Connection which must be closed first. at System.Void MySql.Data.MySqlClient.MySqlCommand.CheckState() at MySqlDataReader MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(System.Data.CommandBehavior behavior) at MySqlDataReader MySql.Data.MySqlClient.MySqlCommand.ExecuteReader()"

代码如下:

public static class MySQL
{
    private static string strConnection;

    static void dbConnection_StateChange(object sender, StateChangeEventArgs ev)
    {
        if (ev.CurrentState == ConnectionState.Broken)
        {
            System.Threading.Thread.Sleep(1000);
            dbConnection.Close();
        }

        if (ev.CurrentState == ConnectionState.Closed)
        {
            System.Threading.Thread.Sleep(1000);

            dbConnection = new MySqlConnection(strConnection);
            dbConnection.StateChange += new System.Data.StateChangeEventHandler(dbConnection_StateChange);
            System.Threading.Thread.Sleep(1000);
            dbConnection.Open();
        }
    }

    private static MySqlConnection dbConnection;
    public static bool openConnection(string dbHost, int dbPort, string dbName, string dbUsername, string dbPassword)
    {
        try
        {
            strConnection = "server=" + dbHost + ";" + "database=" + dbName + ";" + "uid=" + dbUsername + ";" + "password=" + dbPassword;
            dbConnection = new MySqlConnection(strConnection);
            dbConnection.StateChange += new System.Data.StateChangeEventHandler(dbConnection_StateChange);
            dbConnection.Open();
            Console.WriteLine("    Connected to MySQL.");
            return true;
        }
        catch (Exception ex)
        {
            Console.WriteLine("    Couldn't connect to MySQL! The error:");
            Console.WriteLine(ex.Message);
            return false;
        }
    }

    public static void closeConnection()
    {
        try
        {
            dbConnection.Close();
        }
        catch
        {
            Console.WriteLine("tasdsdaa fodaa");
        }
    }

    public static void checkConnection()
    {
        try
        {
        if (dbConnection.State != ConnectionState.Open)
        {
            closeConnection();
            openConnection(Config.dbHost, Config.dbPort, Config.dbName, Config.dbUsername, Config.dbPassword);
        }
        }
        catch {
            Console.WriteLine("ta fodaa");
        }
    }

    public static void runQuery(string Query)
    {
        checkConnection();

        try { new MySqlCommand(Query, dbConnection).ExecuteScalar(); }
        catch { }
    }

    public static int insertGetLast(string Query)
    {
        checkConnection();
        return int.Parse((new MySqlCommand(Query + "; SELECT LAST_INSERT_ID();", dbConnection).ExecuteScalar()).ToString());
    }

    public static string runRead(string Query)
    {
        checkConnection();

        try { return new MySqlCommand(Query + " LIMIT 1", dbConnection).ExecuteScalar().ToString(); }
        catch
        {
            return "";
        }
    }

    public static int runRead(string Query, object Tick)
    {
        checkConnection();

        try { return Convert.ToInt32(new MySqlCommand(Query + " LIMIT 1", dbConnection).ExecuteScalar()); }
        catch
        {
            return 0;
        }
    }

    public static string[] runReadColumn(string Query, int maxResults)
    {
        checkConnection();

        MySqlCommand Command = null;
        MySqlDataReader Reader = null;

        if (maxResults > 0)
            Query += " LIMIT " + maxResults;

        try
        {
            Command = dbConnection.CreateCommand();
            Command.CommandText = Query;
            Reader = Command.ExecuteReader();
            if (Reader.HasRows)
            {
                ArrayList columnBuilder = new ArrayList();
                while (Reader.Read())
                {
                    try { columnBuilder.Add(Reader[0].ToString()); }
                    catch { columnBuilder.Add(""); }
                }
                return (string[])columnBuilder.ToArray(typeof(string));
            }
            else
            {
                return new string[0];
            }
        }
        catch(MySqlException Ex)
        {
            if (Command != null)
            {
                Console.WriteLine("[MySQL] Error!\n\r" + Command.CommandText, Ex);
            }
            else
            {
                Console.WriteLine("[MySQL] Error!", Ex);
            }
        }
        finally
        {
            // Close the reader/command if they are active.
            if (Reader != null)
            {
                Reader.Close();
                Reader.Dispose();
            }
            if (Command != null)
            {
                Command.Dispose();
            }
        }
        return new string[0];
    }

    public static int[] runReadColumn(string Query, int maxResults, object Tick)
    {
        checkConnection();

        MySqlCommand Command = null;
        MySqlDataReader Reader = null;

        if (maxResults > 0)
            Query += " LIMIT " + maxResults;

        try
        {
            Command = dbConnection.CreateCommand();
            Command.CommandText = Query;
            Reader = Command.ExecuteReader();
            if (Reader.HasRows)
            {
                ArrayList columnBuilder = new ArrayList();
                while (Reader.Read())
                {
                    try { columnBuilder.Add(Reader.GetInt32(0)); }
                    catch { columnBuilder.Add(0); }
                }
                return (int[])columnBuilder.ToArray(typeof(int));
            }
            else
            {
                return new int[0];
            }
        }
        catch (MySqlException Ex)
        {
            if (Command != null)
            {
                Console.WriteLine("[MySQL] Error!\n\r" + Command.CommandText, Ex);
            }
            else
            {
                Console.WriteLine("[MySQL] Error!", Ex);
            }
        }
        finally
        {
            // Close the reader/command if they are active.
            if (Reader != null)
            {
                Reader.Close();
                Reader.Dispose();
            }
            if (Command != null)
            {
                Command.Dispose();
            }
        }
        return new int[0];
    }

    public static string[] runReadRow(string Query)
    {
        checkConnection();

        MySqlCommand Command = null;
        MySqlDataReader Reader = null;

        try
        {
            Command = dbConnection.CreateCommand();
            Command.CommandText = Query + " LIMIT 1";
            Reader = Command.ExecuteReader();
            if (Reader.HasRows)
            {
                ArrayList rowBuilder = new ArrayList();
                while (Reader.Read())
                {
                    for (int i = 0; i < Reader.FieldCount; i++)
                    {
                        try { rowBuilder.Add(Reader[i].ToString()); }
                        catch { rowBuilder.Add(""); }
                    }
                }
                return (string[])rowBuilder.ToArray(typeof(string));
            }
            else
            {
                return new string[0];
            }
        }
        catch (MySqlException Ex)
        {
            if (Command != null)
            {
                Console.WriteLine("[MySQL] Error!\n\r" + Command.CommandText, Ex);
            }
            else
            {
                Console.WriteLine("[MySQL] Error!", Ex);
            }
        }
        finally
        {
            // Close the reader/command if they are active.
            if (Reader != null)
            {
                Reader.Close();
                Reader.Dispose();
            }
            if (Command != null)
            {
                Command.Dispose();
            }
        }
        return new string[0];
    }

    public static int[] runReadRow(string Query, object Tick)
    {
        checkConnection();

        MySqlCommand Command = null;
        MySqlDataReader Reader = null;

        try
        {
            Command = dbConnection.CreateCommand();
            Command.CommandText = Query + " LIMIT 1";
            Reader = Command.ExecuteReader();
            if (Reader.HasRows)
            {
                ArrayList rowBuilder = new ArrayList();
                while (Reader.Read())
                {
                    for (int i = 0; i < Reader.FieldCount; i++)
                    {
                        try { rowBuilder.Add(Reader.GetInt32(i)); }
                        catch { rowBuilder.Add(0); }
                    }
                }
                return (int[])rowBuilder.ToArray(typeof(int));
            }
            else
            {
                return new int[0];
            }
        }
        catch (MySqlException Ex)
        {
            if (Command != null)
            {
                Console.WriteLine("[MySQL] Error!\n\r" + Command.CommandText, Ex);
            }
            else
            {
                Console.WriteLine("[MySQL] Error!", Ex);
            }
        }
        finally
        {
            // Close the reader/command if they are active.
            if (Reader != null)
            {
                Reader.Close();
                Reader.Dispose();
            }
            if (Command != null)
            {
                Command.Dispose();
            }
        }
        return new int[0];
    }


    public static bool checkExists(string Query)
    {
        checkConnection();
        try { return new MySqlCommand(Query + " LIMIT 1", dbConnection).ExecuteReader().HasRows; }
        catch
        {
            return false;
        }
    }

    public static List<List<string>> readArray(string Query)
    {
        MySqlCommand Command = null;
        MySqlDataReader Reader = null;
        try
        {
            // Create the command.
            Command = MySQL.dbConnection.CreateCommand();
            Command.CommandText = Query;

            // Read the result.
            Reader = Command.ExecuteReader();

            // Store the incomming fields.
            List<List<string>> fieldValues = new List<List<string>>();

            // Read all the data.
            while (Reader.Read())
            {
                // Create a new field values to hold the data.
                List<string> Buffer = new List<string>();

                // Add the field values.
                for (int i = 0; i < Reader.FieldCount; i++)
                {
                    Buffer.Add(Reader[i].ToString());
                }

                // Add it too our overall data.
                fieldValues.Add(Buffer);
            }
            return fieldValues;
        }
        catch (MySqlException Ex)
        {
            if (Command != null)
            {
                Console.WriteLine("[MySQL] Error!\n\r" + Command.CommandText, Ex);
            }
            else
            {
                Console.WriteLine("[MySQL] Error!", Ex);
            }
            return null;
        }
        finally
        {
            // Close the reader/command if they are active.
            if (Reader != null)
            {
                Reader.Close();
                Reader.Dispose();
            }
            if (Command != null)
            {
                Command.Dispose();
            }
        }
    }


    public static string Stripslash(string Query)
    {
        try { return Query.Replace(@"\", "\\").Replace("'", @"\'"); }
        catch { return ""; }
    }
}

Answer 1

您需要在 Reader 对象上调用 Close 来释放下划线资源，如下所示:

    try
    {
        Command = dbConnection.CreateCommand();
        Command.CommandText = Query;
        using (Reader = Command.ExecuteReader()) // 'using' forces a call to `Dispose`/`Close` at the end of the block
        {
            if (Reader.HasRows)
            {
                ArrayList columnBuilder = new ArrayList();
                while (Reader.Read())
                {
                    try { columnBuilder.Add(Reader.GetInt32(0)); }
                    catch { columnBuilder.Add(0); }
                }
                return (int[])columnBuilder.ToArray(typeof(int));
            }
            else
            {
                return new int[0];
            }
        }
    }