Question

我目前正在创建存储停车信息的数据库。现在我能够成功连接到数据库并添加一个条目，然后添加另一个条目等。但是，当我在Access中查看表时，我看不到我在每个记录中输入的内容以及当我查看表时在Visual Studio中，它将每条记录显示为Null。

我做错了什么？我不仅对编程而且对数据库也很新。

以下是我的应用的代码：

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 System.Data.OleDb;
using System.Data;
using System.ComponentModel;


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

    public MainWindow()
    {
        InitializeComponent();
    }


    private void btnSave_Click(object sender, RoutedEventArgs e)
    {
        using (OleDbConnection DBConnect = new OleDbConnection())
        {
            DBConnect.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source = C:\Users\bkoso\documents\visual studio 2015\Projects\ParkingDatabase\ParkingDatabase\ParkingData.accdb";
            OleDbCommand com = new OleDbCommand();
            if (DBConnect.State == ConnectionState.Open)
            {
                OleDbCommand com1 = new OleDbCommand("INSERT INTO [Guest Info]([Guest First Name], [Guest Last Name], [Room Number], [Departure Date], [Return Date], [Vehicle Colour], [Vehicle Make], [Plate Number], [Contact First Name], [Contact Last Name], [Contact Number], [Contact Email], [Tag Number]) Values(@[Guest First Name], @[Guest Last Name], @[Room Number], @[Departure Date], @[Return Date], @[Vehicle Colour], @[Vehicle Make], @[Plate Number], @[Contact First Name], @[Contact Last Name], @[Contact Email], @[Contact Email], @[Tag Number])", DBConnect);
                com1.Parameters.AddWithValue("@[Guest First Name]", txtBxGstFName.Text);
                com1.Parameters.AddWithValue("@[Guest Last Name]", txtBxGstLName.Text);
                com1.Parameters.AddWithValue("@[Room Number]", txtBxRm.Text);
                com1.Parameters.AddWithValue("@[Departure Date]", txtBxDDate.Text);
                com1.Parameters.AddWithValue("@[Return Date]", txtBxRDate.Text);
                com1.Parameters.AddWithValue("@[Vehicle Colour]", txtBxVColour.Text);
                com1.Parameters.AddWithValue("@[Vehicle Make]", txtBxVMake.Text);
                com1.Parameters.AddWithValue("@[Plate Number]", txtBxPlate.Text);
                com1.Parameters.AddWithValue("@[Contact First Name]", txtBxContactFName.Text);
                com1.Parameters.AddWithValue("@[Contact Last Name]", txtBxContactLName.Text);
                com1.Parameters.AddWithValue("@[Contact Number]", txtBxPhone.Text);
                com1.Parameters.AddWithValue("@[Contact Email]", txtBxEmail.Text);
                com1.Parameters.AddWithValue("@[Tag Number]", txtBxTag.Text);
            }
            else
            {
                DBConnect.Open();
                OleDbCommand com2 = new OleDbCommand("INSERT INTO [Guest Info]([Guest First Name], [Guest Last Name], [Room Number], [Departure Date], [Return Date], [Vehicle Colour], [Vehicle Make], [Plate Number], [Contact First Name], [Contact Last Name], [Contact Number], [Contact Email], [Tag Number]) Values(@[Guest First Name], @[Guest Last Name], @[Room Number], @[Departure Date], @[Return Date], @[Vehicle Colour], @[Vehicle Make], @[Plate Number], @[Contact First Name], @[Contact Last Name], @[Contact Email], @[Contact Email], @[Tag Number])", DBConnect);
                com2.Parameters.AddWithValue("@[Guest First Name]", txtBxGstFName.Text);
                com2.Parameters.AddWithValue("@[Guest Last Name]", txtBxGstLName.Text);
                com2.Parameters.AddWithValue("@[Room Number]", txtBxRm.Text);
                com2.Parameters.AddWithValue("@[Departure Date]", txtBxDDate.Text);
                com2.Parameters.AddWithValue("@[Return Date]", txtBxRDate.Text);
                com2.Parameters.AddWithValue("@[Vehicle Colour]", txtBxVColour.Text);
                com2.Parameters.AddWithValue("@[Vehicle Make]", txtBxVMake.Text);
                com2.Parameters.AddWithValue("@[Plate Number]", txtBxPlate.Text);
                com2.Parameters.AddWithValue("@[Contact First Name]", txtBxContactFName.Text);
                com2.Parameters.AddWithValue("@[Contact Last Name]", txtBxContactLName.Text);
                com2.Parameters.AddWithValue("@[Contact Number]", txtBxPhone.Text);
                com2.Parameters.AddWithValue("@[Contact Email]", txtBxEmail.Text);
                com2.Parameters.AddWithValue("@[Tag Number]", txtBxTag.Text);
            }


            if (DBConnect.State == ConnectionState.Open)
            {
                //com.ExecuteNonQuery();
            }
                MessageBox.Show("Guest Information Saved Successfully");
                txtBxGstFName.Text = "";
                txtBxGstLName.Text = "";
                txtBxRm.Text = "";
                txtBxDDate.Text = "";
                txtBxRDate.Text = "";
                txtBxVColour.Text = "";
                txtBxVMake.Text = "";
                txtBxPlate.Text = "";
                txtBxContactFName.Text = "";
                txtBxContactLName.Text = "";
                txtBxPhone.Text = "";
                txtBxEmail.Text = "";
                txtBxTag.Text = "";
        }
    }    

    private void btnClear_Click(object sender, RoutedEventArgs e)
    {
        txtBxGstFName.Text = "";
        txtBxGstLName.Text = "";
        txtBxRm.Text = "";
        txtBxDDate.Text = "";
        txtBxRDate.Text = "";
        txtBxVColour.Text = "";
        txtBxVMake.Text = "";
        txtBxPlate.Text = "";
        txtBxContactFName.Text = "";
        txtBxContactLName.Text = "";
        txtBxPhone.Text = "";
        txtBxEmail.Text = "";
        txtBxTag.Text = "";
    }

    private void btnView_Click(object sender, RoutedEventArgs e)
    {

    }

    private void btnSame_Click(object sender, RoutedEventArgs e)
    {

    }

    private void txtBoxGuestFirstName_TextChanged(object sender, TextChangedEventArgs e)
    {

    }

    private void btnDelete_Click(object sender, RoutedEventArgs e)
    {

    }

    private void btnSearch_Click(object sender, RoutedEventArgs e)
    {

    }
}
}

非常感谢任何帮助。

Bloodstalker

Answer 1

以下是我可以立即看到的一些问题

您每次都创建一个新连接 - 这是正确的 - 但其状态永远不会是Open
您将com初始化为命令，但从不使用它。没有配置参数
您初始化com1和com2设置其参数，但从不执行其中任何一个
您实际执行com的行已被注释掉。

您应初始化com，设置其参数，打开连接，然后致电ExecuteNonQuery并撤消设置com1和com2的所有代码 - 两者均为无关紧要和不必要的。

例如：

using (OleDbConnection DBConnect = new OleDbConnection())
{
      DBConnect.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source = C:\Users\bkoso\documents\visual studio 2015\Projects\ParkingDatabase\ParkingDatabase\ParkingData.accdb";
     using(OleDbCommand com = new OleDbCommand("INSERT INTO [Guest Info]([Guest First Name], [Guest Last Name], [Room Number], [Departure Date], [Return Date], [Vehicle Colour], [Vehicle Make], [Plate Number], [Contact First Name], [Contact Last Name], [Contact Number], [Contact Email], [Tag Number]) Values(@[Guest First Name], @[Guest Last Name], @[Room Number], @[Departure Date], @[Return Date], @[Vehicle Colour], @[Vehicle Make], @[Plate Number], @[Contact First Name], @[Contact Last Name], @[Contact Email], @[Contact Email], @[Tag Number])", DBConnect))
     {
       com.Parameters.AddWithValue("@[Guest First Name]", txtBxGstFName.Text);
       com.Parameters.AddWithValue("@[Guest Last Name]", txtBxGstLName.Text);
       // .. snip other params .. //
       DBConnect.Open();
       com.ExecuteNonQuery();
       DBConnect.Close();
     }
}

顺便说一句，您不应该对连接字符串进行硬编码，而是从配置文件中读取它。

Answer 2

您的命令已设置，但您永远不会执行查询。执行是您实际运行查询命令并将记录保存在数据库中所需的。您需要根据需要致电com1.ExecuteNonQuery()或com2.ExecuteNonQuery()。

您最有可能将方法缩减为以下内容：

    private void btnSave_Click(object sender, RoutedEventArgs e)
{
    using (OleDbConnection DBConnect = new OleDbConnection())
    {
        DBConnect.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source = C:\Users\bkoso\documents\visual studio 2015\Projects\ParkingDatabase\ParkingDatabase\ParkingData.accdb";
        OleDbCommand com = new OleDbCommand("INSERT INTO [Guest Info]([Guest First Name], [Guest Last Name], [Room Number], [Departure Date], [Return Date], [Vehicle Colour], [Vehicle Make], [Plate Number], [Contact First Name], [Contact Last Name], [Contact Number], [Contact Email], [Tag Number]) Values(@[Guest First Name], @[Guest Last Name], @[Room Number], @[Departure Date], @[Return Date], @[Vehicle Colour], @[Vehicle Make], @[Plate Number], @[Contact First Name], @[Contact Last Name], @[Contact Email], @[Contact Email], @[Tag Number])", DBConnect);
        com.Parameters.AddWithValue("@[Guest First Name]", txtBxGstFName.Text);
        com.Parameters.AddWithValue("@[Guest Last Name]", txtBxGstLName.Text);
        com.Parameters.AddWithValue("@[Room Number]", txtBxRm.Text);
        com.Parameters.AddWithValue("@[Departure Date]", txtBxDDate.Text);
        com.Parameters.AddWithValue("@[Return Date]", txtBxRDate.Text);
        com.Parameters.AddWithValue("@[Vehicle Colour]", txtBxVColour.Text);
        com.Parameters.AddWithValue("@[Vehicle Make]", txtBxVMake.Text);
        com.Parameters.AddWithValue("@[Plate Number]", txtBxPlate.Text);
        com.Parameters.AddWithValue("@[Contact First Name]", txtBxContactFName.Text);
        com.Parameters.AddWithValue("@[Contact Last Name]", txtBxContactLName.Text);
        com.Parameters.AddWithValue("@[Contact Number]", txtBxPhone.Text);
        com.Parameters.AddWithValue("@[Contact Email]", txtBxEmail.Text);
        com.Parameters.AddWithValue("@[Tag Number]", txtBxTag.Text);

        // don't forget to execute the query!
        com.ExecuteNonQuery();

        MessageBox.Show("Guest Information Saved Successfully");
        txtBxGstFName.Text = "";
        txtBxGstLName.Text = "";
        txtBxRm.Text = "";
        txtBxDDate.Text = "";
        txtBxRDate.Text = "";
        txtBxVColour.Text = "";
        txtBxVMake.Text = "";
        txtBxPlate.Text = "";
        txtBxContactFName.Text = "";
        txtBxContactLName.Text = "";
        txtBxPhone.Text = "";
        txtBxEmail.Text = "";
        txtBxTag.Text = "";
    }
}

使用C＃将所有条目的Null值转换为访问数据库。为什么？

2 个答案: