Question

我正在尝试制作一个程序时出现问题，这是为了检查一个mysql数据库以查看该名称的用户是否已经退出，如果它没有，它应该创建一个，如果是，它应该显示错误提示。

没有编译错误，它已经到达代码的末尾，告诉我＆＃34;用户已创建＆＃34;但没有数据添加到数据库，不知道我在哪里出错了，谢谢！

 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 System.Net;
    using MySql.Data.MySqlClient;

    namespace Oswald
    {
        public partial class frmRegister : Form
        {
            public frmRegister()
            {
                InitializeComponent();
            }

            private void btnRegister_Click(object sender, EventArgs e)
            {
                    String mysqlConnectionString = "Server=sql3.freesqldatabase.com;Database=sql367701;UID=sql367701;Password=*****;Port=3306";
                    MySqlConnection connection = new MySqlConnection(mysqlConnectionString);
                    connection.Open();

                    string query = "SELECT * FROM UserInfo WHERE Username='" + txtUsername.Text + "'";
                    bool exists = false;

                    MySqlCommand cmd = new MySqlCommand(query, connection);
                    MySqlDataReader reader = cmd.ExecuteReader();

                    while (reader.Read())
                    {
                        if(txtUsername.Text == reader.GetString("Username"))
                        {
                            MessageBox.Show("User Already Exits", "Oswald", MessageBoxButtons.OK, MessageBoxIcon.Error);
                            exists = true;
                        }
                        else { exists = false; }
                    }

                    reader.Close();

                    if (exists == false)
                    {
                        query = "INSERT INTO UserInfo (Username, Password, Email, IP) VALUES (@username, @password, @ip);";

                        string ip = new WebClient().DownloadString(@"http://icanhazip.com").Trim();

                        using (MySqlCommand cmd2 = new MySqlCommand(query, connection))
                        {
                            cmd.Parameters.AddWithValue("@username", txtUsername.Text);
                            cmd.Parameters.AddWithValue("@password", txtPassword.Text);
                            cmd.Parameters.AddWithValue("@email", txtEmail.Text);
                            cmd.Parameters.AddWithValue("@ip", ip);
                            cmd.ExecuteNonQuery();
                        }

                        MessageBox.Show("Account Created!", "Oswald", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        this.Close();
                    }
                }
            }
        }

Answer 1

您在插入声明中缺少电子邮件。它应该是cmd2。你正在查询cmd

query = "INSERT INTO UserInfo (Username, Password, Email, IP) VALUES (@username, @password, @email, @ip)";
using (MySqlCommand cmd2 = new MySqlCommand(query, connection))
{
  cmd2.Parameters.AddWithValue("@username", txtUsername.Text);
  cmd2.Parameters.AddWithValue("@password", txtPassword.Text);
  cmd2.Parameters.AddWithValue("@email", txtEmail.Text);
  cmd2.Parameters.AddWithValue("@ip", ip);
      int rows = cmd.ExecuteNonQuery();
      if(rows > 0)
            MessageBox.Show("insert OK...");
}

Answer 2

我认为您在将详细信息保存到数据库时使用的是cmd而不是cmd2。：）

Answer 3

另外，您可以在代码中使用简短版本;）

                string query = "SELECT COUNT(*) FROM UserInfo WHERE Username='" + txtUsername.Text + "'";

                MySqlCommand cmd = new MySqlCommand(query, connection);

                if (cmd.ExecuteScalar()>0)
                {
                        MessageBox.Show("User Already Exits", "Oswald", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
                else
                {
                       query = "INSERT INTO UserInfo (Username, ...

或者您可能为UserInfo添加唯一索引。

C＃MySql数据未正确写入/读取

3 个答案: