C# 数据读取器错误

Question

我在论坛上寻找这个问题的解决方案，但没有找到适合我的问题的解决方案。单击按钮时，我收到错误消息：

There is already an open DataReader associated with this Connection which must be closed first.

因此，我尝试在使用后关闭所有 DataReader，我尝试使用 CommandBehavior，但其中 none 有效。我尝试使用 using(MysqlCommand...) 但没有用。我能做些什么？最奇怪的是代码可以正常工作，但每次按下按钮后，我都会再次收到该错误。有什么想法吗？

请不要将问题标记为重复问题，我知道此处存在问题，但我想我的问题缺少答案。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using MySql.Data.MySqlClient;
using System.Drawing.Text;

namespace simulator
{
    public partial class Simulare : Form
    {
        public int corect = 0, incorect = 0;
        Timer timer;
        static string dataA = "SELECT DISTINCT * FROM questions order by rand() limit 1";
        public int r1;
        public int r2;
        public int r3;
        public Simulare()
        {
            InitializeComponent();
            this.FormClosing += Form1_FormClosing;
            label1.Text = TimeSpan.FromMinutes(30).ToString("mm\:ss");
            label10.Text = corect.ToString();
            label12.Text = incorect.ToString();
            //FormBorderStyle = FormBorderStyle.None;
            WindowState = FormWindowState.Maximized;
        }
        private void simulare_Load(object sender, EventArgs e)
        {
            var startTime = DateTime.Now;
            timer = new Timer() { Interval = 1000 };
            timer.Tick += (obj, args) =>
            {
                TimeSpan ts = TimeSpan.FromMinutes(30) - (DateTime.Now - startTime);
                label1.Text = ts.ToString("mm\:ss");
                if (ts.Minutes == 00 && ts.Seconds == 00)
                {
                    timer.Stop();
                    MessageBox.Show("Timpul a expirat. Ai picat!");
                    MySqlCommand upd = new MySqlCommand("select totalno from accounts where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection());
                        try
                        {
                            MySqlDataReader upad = upd.ExecuteReader();
                                while (upad.Read())
                                {
                                    int totalnu = (int)upad["totalno"];
                                    totalnu++;
                                    using (MySqlCommand update = new MySqlCommand("UPDATE accounts SET totalno=@totalnu where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection()))
                                    {
                                        update.Parameters.AddWithValue("@totalnu", totalnu);
                                        int rows = update.ExecuteNonQuery();
                                    }
                                }
                                upad.Close();
                        }
                        catch (Exception ex2)
                        {
                            MessageBox.Show(ex2.Message);
                        }
                    }
            };
            timer.Start();
            select();
        }

        private void select()
        {
            using (ConnConfig.getConnection())
            {
                MySqlCommand cmd = new MySqlCommand(dataA, ConnConfig.getConnection());
                cmd.CommandType = CommandType.Text;
                MySqlDataReader rdra = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                try
                {
                    while (rdra.Read())
                    {
                        label2.Text = rdra["question"].ToString();
                        label3.Text = rdra["answer1"].ToString();
                        label4.Text = rdra["answer2"].ToString();
                        label5.Text = rdra["answer3"].ToString();
                        r1 = (int)rdra["option1"];
                        r2 = (int)rdra["option2"];
                        r3 = (int)rdra["option3"];
                    }
                    rdra.Close();
                }
                catch (InvalidOperationException ex)
                {
                    MessageBox.Show(ex.Message);
                }
                finally
                {
                    ConnConfig.closeConn();
                }
            }
        }
        private void button1_Click(object sender, EventArgs e)
        {
            int result1 = checkBox1.CheckState == CheckState.Checked ? 1 : 0;
            int result2 = checkBox2.CheckState == CheckState.Checked ? 1 : 0;
            int result3 = checkBox3.CheckState == CheckState.Checked ? 1 : 0;
            using(ConnConfig.getConnection())
            {
                MySqlCommand cmd = new MySqlCommand(dataA, ConnConfig.getConnection());
                cmd.CommandType = CommandType.Text;
                MySqlDataReader rdr = cmd.ExecuteReader();
                try
                {
                    while (rdr.Read())
                    {
                        if (checkBox1.Checked == false && checkBox2.Checked == false && checkBox3.Checked == false)
                        {
                            MessageBox.Show("Bifati minim o casuta!");
                            return;
                        }
                        else
                        {
                            if ((result1 == r1) && (result2 == r2) && (result3 == r3))
                            {
                                corect++;
                                label10.Text = corect.ToString();
                                checkBox1.Checked = false;
                                checkBox2.Checked = false;
                                checkBox3.Checked = false;
                                select();
                            }
                            else
                            {
                                incorect++;
                                label12.Text = incorect.ToString();
                                checkBox1.Checked = false;
                                checkBox2.Checked = false;
                                checkBox3.Checked = false;
                                select();
                            }
                            if (corect + incorect == 26)
                            {
                                int totalalll;
                                timer.Stop();
                                button1.Enabled = false;
                                MySqlCommand upd = new MySqlCommand("select * from accounts where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection());
                                MySqlDataReader upad = upd.ExecuteReader();
                                while (upad.Read())
                                {
                                    totalalll = (int)upad["totalall"];
                                    totalalll++;
                                    using (MySqlCommand update = new MySqlCommand("UPDATE accounts SET totalall=@totalalll where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection()))
                                    {
                                        update.Parameters.AddWithValue("@totalalll", totalalll);
                                        Int32 rows = update.ExecuteNonQuery();
                                    }
                                }
                                upad.Close();
                            }
                            if (corect == 26)
                            {
                                MySqlCommand upd = new MySqlCommand("select totalyes from accounts where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection());
                                MySqlDataReader upad = upd.ExecuteReader();
                                while (upad.Read())
                                {
                                    int totalda = (Int32)upad["totalyes"];
                                    totalda++;
                                    using (MySqlCommand update = new MySqlCommand("UPDATE accounts SET totalyes=@totalda where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection()))
                                    {
                                        update.Parameters.AddWithValue("@totalda", totalda);
                                        int rows = update.ExecuteNonQuery();
                                    }
                                }
                                upad.Close();
                                MessageBox.Show("Bravos");
                            }
                            else
                            {
                                MySqlCommand upd = new MySqlCommand("select totalno from accounts where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection());
                                MySqlDataReader upad = upd.ExecuteReader();
                                while (upad.Read())
                                {
                                    int totalnu = (int)upad["totalno"];
                                    totalnu++;
                                    using (MySqlCommand update = new MySqlCommand("UPDATE accounts SET totalno=@totalnu where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection()))
                                    {
                                        update.Parameters.AddWithValue("@totalnu", totalnu);
                                        int rows = update.ExecuteNonQuery();
                                    }
                                }
                                upad.Close();
                                MessageBox.Show("Mai invata!");
                            }
                        }
                    }
                    rdr.Close();
                }
                catch (MySqlException ex)
                {
                    MessageBox.Show(ex.Message);
                }
                finally
                {
                    ConnConfig.closeConn();
                }
            }
        }

        private void Form1_FormClosing(Object sender, FormClosingEventArgs e)
        {
            if (e.CloseReason == CloseReason.WindowsShutDown) return;

            if (this.DialogResult == DialogResult.Cancel)
            {
                e.Cancel = false;
                timer.Stop();
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }
}

class ConnConfig
    {
        private static string conn = "string connection";
        public static MySqlConnection connect;

        private ConnConfig()
        {

        }
        public static MySqlConnection getConnection()
        {
            if(connect !=null){

                return connect;
            }
            else 
                try{
                    connect = new MySqlConnection(conn);
                    connect.Open();
                    return connect;
                }
            catch(MySqlException e){
                throw new Exception("Cannot connect",e);
            }
        }
        public static void closeConn()
        {
            connect.Close();
        }
        public static void openConn()
        {
            connect.Open();
        }
    }

Answer 1

您的异常的根本原因是您正在执行其他查询，同时您仍在迭代先前查询的结果。如果您对嵌套查询使用相同的连接，那么您不应该像现在这样嵌套查询。

Answer 2

您正在使用 reader 从 SQLCommand upd 获取数据。

那么你读的是值。

之后您将使用另一个 SqlCommand 'update' 来更新结果..

即使您使用两个不同的 SQLCommand，您也使用相同的连接。那就是问题所在。为第二个 SQLCommand 使用单独的连接，您的问题将得到解决。

试试这个。

行后

MessageBox.Show("Timpul a expirat. Ai picat!");

加个赞

MessageBox.Show("Timpul a expirat. Ai picat!");
MySqlConnection conn1 = ConnConfig.getConnection();
MySqlConnection conn2 = new MySqlConnection();
conn2.ConnectionString = conn1.ConnectionString;
conn2.Open();

然后在行

MySqlCommand upd = new MySqlCommand("select totalno from accounts where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection());

换个赞

MySqlCommand upd = new MySqlCommand("select totalno from accounts where username = '" + Index.textBox1.Text + "'", conn1);

并在行

using (MySqlCommand update = new MySqlCommand("UPDATE accounts SET totalno=@totalnu where username = '" + Index.textBox1.Text + "'", ConnConfig.getConnection()))

换个赞

using (MySqlCommand update = new MySqlCommand("UPDATE accounts SET totalno=@totalnu where username = '" + Index.textBox1.Text + "'", conn2))

Answer 3

更改 getConnection 函数

public static MySqlConnection getConnection()
    {
        MySqlConnection connect = null;
        try
        {
            connect = new MySqlConnection(connect);
            connect.Open();
            return connect;
        }
        catch (MySqlException e)
        {
            throw new Exception("Cannot connect", e);
        }
    }

让所有其他代码保持原样

C# 数据读取器错误

C# DataReader error

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mysqldatareader