Question

我目前正在尝试使用C＃语言的Visual Studios WPF应用程序创建一个登录系统。每次Login_Button_Click函数运行时，我都会收到一条错误消息。错误消息显示特定的代码行var DataReader = TeacherLoginsCommand.ExecuteReader();

我检查了无数的视频，很多视频似乎都在做同样的事情而没有任何问题。任何帮助表示赞赏。

C＃代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using MySql.Data.MySqlClient;
using System.Data;

namespace WpfApp1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow(){

            InitializeComponent();
        }

        //When Login Button Is Clicked Do:
        private void Login_Button_Click(Object sender, RoutedEventArgs e){

            //Gets Username And Password From Loing Screen
            string TeacherID = Teacher_ID.Text;
            string TeacherPassword = Teacher_Password.Password;

            //Connects To Database And Gets All Teacher Logins
            string connectionString = "SERVER=localhost;DATABASE=teacherlogins;UID=root;PASSWORD=Password";
            MySqlConnection TeacherLoginsConnection = new MySqlConnection(connectionString);
            string CurrentQuery = "SELECT * from teacherloginstable where ID = " + Teacher_ID;
            MySqlCommand TeacherLoginsCommand = new MySqlCommand(CurrentQuery, TeacherLoginsConnection);

            TeacherLoginsConnection.Open();
            var DataReader = TeacherLoginsCommand.ExecuteReader();
            DataTable TeacherLoginsTable = new DataTable();
            TeacherLoginsTable.Load(DataReader);
            TeacherLoginsConnection.Close();

            if (TeacherLoginsTable.Rows.Contains(TeacherPassword))
            {

                MessageBox.Show("Login Sucsessful", "Welcome" + Teacher_ID);


            }
            else {

                MessageBox.Show("Details Not Recognised", "Error: Details Not Recognised");

            }

        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {

        }
    }
}

XAML代码：

<Window x:Class="WpfApp1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:WpfApp1"
    mc:Ignorable="d"
    Title="Alperton Login" Height="450" Width="625">
<Border Padding="50">
    <StackPanel Margin="5">
        <Image Source="download.png" Height="90" Margin="0, 0, 0, 20"/>

        <TextBlock Text="Teacher ID" FontWeight="Bold" FontSize="20" Padding="0,10"/>
        <TextBox Padding="5" x:Name="Teacher_ID"/>

        <TextBlock Text="Teacher Password" FontWeight="Bold" FontSize="20" Padding="0,10"/>
        <PasswordBox Padding="5" x:Name="Teacher_Password" />

        <Button Content="Login" Margin="0,10" Padding="0, 3" FontWeight="Bold" FontSize="15" Click="Login_Button_Click"/>

    </StackPanel>
</Border>

错误讯息：

MySql.Data.MySqlClient.MySqlException: 'You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '.TextBox' at line 1'

Answer 1

而不是：

string TeacherID = Teacher_ID.Text;

写

int TeacherID = Convert.toInt32(Teacher_ID.Text);

Answer 2

Teacher_ID是XAML代码中的TextBox id（x：Name），它引用TextBox。您必须在sql语句中发送其text属性。

Sql语句必须是这样的 SELECT * FROM teacherloginstable where ID = " + Teacher_ID.Text;

Answer 3

你是自己不幸决定给出两个不同目的非常相似的变量的受害者。

您有一个名为Teacher_ID的文本框，并将其文本放在TeacherID中。你有可能在查询中使用了错误的吗？

您是否尝试使用调试器或Debug.WriteLine或Console.WriteLine检查要发送给MySQL的SQL查询字符串？我希望你能看到如下内容：

SELECT * from teacherloginstable where ID = System.Windows.Controls.TextBox

（System.Windows.Controls.TextBox是您在ToString()上致电TextBox时获得的。）

你看到了问题吗？

您可以使用正确的变量名

来修复它

       string CurrentQuery = "SELECT * from teacherloginstable where ID = " + TeacherID;

但实际上，请不要这样做。请不要通过连接值来构建SQL字符串。使用参数化SQL要好得多：

        string CurrentQuery = "SELECT * from teacherloginstable where ID = @teacherID";
        MySqlCommand TeacherLoginsCommand = new MySqlCommand(CurrentQuery, TeacherLoginsConnection);
        TeacherLoginsCommand.Parameters.AddWithValue("@teacherID", TeacherID);

C＃MySQL阅读器错误 - ＆＃34; Sql语法错误＆＃34;

3 个答案: