C#学习(九)——数据库与WPF

一、创建WPF项目链接数据库

首先创建WPF项目，在nuget安装包中下载System.Data.SqlClient

配置数据库的连接字符串来连接数据库
创建示例数据库，拥有两个table：

CREATE TABLE [dbo].[Customers] (
    [Id]       INT         IDENTITY (1, 1) NOT NULL,
    [Name]     NCHAR (50)  NOT NULL,
    [IdNumber] NCHAR (18)  NOT NULL,
    [Address]  NCHAR (100) NOT NULL,
    PRIMARY KEY CLUSTERED ([Id] ASC)
);

CREATE TABLE [dbo].Appointments
(
	[Id] INT NOT NULL PRIMARY KEY IDENTITY, 
    [Time] DATETIME NOT NULL, 
    [CustomerId] INT NOT NULL, 
    CONSTRAINT [FK_Appointments_Customers] FOREIGN KEY (CustomerId) REFERENCES Customers(Id)
)

实现UI界面对于数据库数据的显示
MainWindow.xaml.cs

public partial class MainWindow : Window
{
    private SqlConnection _sqlConnection;
    public MainWindow()
    {
        InitializeComponent();
        string connectionString = "数据库连接字符串";//填入自己的数据库连接字符串

        _sqlConnection = new SqlConnection(connectionString);

        ShowCustomers();
    }

    //访问数据库
    private void ShowCustomers()
    {
        //防止数据库死机等意外导致以下操作全部失败,系统崩溃
        try
        {
            SqlDataAdapter adapter = new SqlDataAdapter("select * from Customers", _sqlConnection);
            //数据库适配器可以帮我们解决数据库的打开关闭
            using (adapter)
            {
                DataTable customerTable = new DataTable();
                adapter.Fill(customerTable);

                customerList.DisplayMemberPath = "Name";
                //绑定数据
                customerList.SelectedValuePath = "Id";
                //绑定数据源
                customerList.ItemsSource = customerTable.DefaultView;
            }
        }catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }        
    }

	private void customerList_SelectionChanged(object sender, SelectionChangedEventArgs e)
	{
	    try
	    {
	        //查询Appointments.CustomerId = Customers.Id且为参数传入的Id，@为参数引导
	        string query = "select * from Appointments join Customers on Appointments.CustomerId = Customers.Id where Customers.Id = @CustomerId";
	
	        var customerId = customerList.SelectedValue;
	        //用于删除预约信息时，会先删除customerId，造成customerId为空情况
	        if (customerId == null)
	        {
	            appointmentList.ItemsSource = null;
	            return;
	        }        
	
	        SqlCommand sqlCommand = new SqlCommand(query, _sqlConnection);
	
	        SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(sqlCommand);
	        //键值对数据在此聚合
	        sqlCommand.Parameters.AddWithValue("@CustomerId", customerId);
		
	        using (sqlDataAdapter)
	        {
	            DataTable appointmentTable = new DataTable();
	            sqlDataAdapter.Fill(appointmentTable);
	
	            appointmentList.DisplayMemberPath = "Time";
	            //绑定数据
	            appointmentList.SelectedValuePath = "Id";
	            //绑定数据源
	            appointmentList.ItemsSource = appointmentTable.DefaultView;
	        }
	    }
	    catch (Exception ex)
	    {
	        MessageBox.Show(ex.ToString());
	    }
	}
}

注意，要使用一个try,catch来包含操作，防止因为数据库卡顿死机等问题造成系统瘫痪

示例UI界面如下，注意UI界面的命名与后面函数名的对应

<Grid>
    <Label Content="客户列表" HorizontalAlignment="Left" Margin="67,35,0,0" VerticalAlignment="Top" Width="219"/>
    <ListBox d:ItemsSource="{d:SampleData ItemCount=5}" Margin="67,91,730,202" Name="customerList" SelectionChanged="customerList_SelectionChanged"/>
    <Label Content="预约记录" HorizontalAlignment="Left" Margin="590,30,0,0" VerticalAlignment="Top" Width="219"/>
    <ListBox d:ItemsSource="{d:SampleData ItemCount=5}" Margin="590,91,191,202" Name="appointmentList"/>
    <Button Content="删除客户" HorizontalAlignment="Left" Margin="67,388,0,0" VerticalAlignment="Top" RenderTransformOrigin="6.484,2.324" Width="203" Click="DeleteCustomer_Click"/>
    <Button Content="取消预约" HorizontalAlignment="Left" Margin="590,388,0,0" VerticalAlignment="Top" Width="219" Click="CancelAppointment_Click"/>
    <TextBox Name="NameTextBox" HorizontalAlignment="Left" Margin="23,495,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
    <TextBox Name="IdTextBox" HorizontalAlignment="Left" Margin="148,495,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
    <TextBox Name="AddressTextBox" HorizontalAlignment="Left" Margin="278,495,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
    <Label Content="姓名	" HorizontalAlignment="Left" Margin="23,466,0,0" VerticalAlignment="Top"/>
    <Label Content="身份证号" HorizontalAlignment="Left" Margin="148,466,0,0" VerticalAlignment="Top"/>
    <Label Content="住址" HorizontalAlignment="Left" Margin="278,466,0,0" VerticalAlignment="Top" RenderTransformOrigin="-1.766,1.797"/>
    <Label Content="添加客户信息" HorizontalAlignment="Left" Margin="23,436,0,0" VerticalAlignment="Top"/>
    <Button Content="添加客户" HorizontalAlignment="Left" Margin="23,533,0,0" VerticalAlignment="Top" Click="AddCustomer_Click"/>
    <DatePicker Name="AppointmentDatePicker" HorizontalAlignment="Left" Margin="590,479,0,0" VerticalAlignment="Top"/>
    <Label Content="添加预约日期" HorizontalAlignment="Left" Margin="590,436,0,0" VerticalAlignment="Top"/>
    <Button Content="预约" HorizontalAlignment="Left" Margin="590,523,0,0" VerticalAlignment="Top" Click="AddAppointment_Click"/>
    <Button Content="更新客户资料" HorizontalAlignment="Left" Margin="163,538,0,0" VerticalAlignment="Top" Click="UpdateCustomer_Click"/>
Grid>

二、实现UI页面对于数据库的【增、删、改】

1.实现删除
对于Appointments表的删除，只需要直接delete即可以完成
示例代码如下

private void CancelAppointment_Click(object sender, RoutedEventArgs e)
{
    try
    {
        var sql = "delete from Appointments where Id = @AppointmentId";
        var appointmentId = appointmentList.SelectedValue;

        SqlCommand sqlCommand = new SqlCommand(sql, _sqlConnection);
        sqlCommand.Parameters.AddWithValue("@AppointmentId", appointmentId);

        _sqlConnection.Open();
        //执行删除
        sqlCommand.ExecuteScalar();
        MessageBox.Show("取消预约成功！");

    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
    finally
    {
        _sqlConnection.Close();
        //刷新预约列表
        customerList_SelectionChanged(null, null);
    }
}

对于Customers表的删除，由于Appointments表的CustomerId为对应Customers表Id的外键，因此删除时，需要先删除Appointments数据，再删除Customers表的数据

private void DeleteCustomer_Click(object sender, RoutedEventArgs e)
{
    try
    {
        string sqlDelteAppointment = "delete from Appointments where CustomerId = @CustomerId";
        string sqlDeleteCustomer = "delete from Customers where Id = @CustomerId";

        var customerId = customerList.SelectedValue;

        SqlCommand sqlCommand1 = new SqlCommand( sqlDelteAppointment, _sqlConnection);
        SqlCommand sqlCommand2 = new SqlCommand( sqlDeleteCustomer, _sqlConnection);

        sqlCommand1.Parameters.AddWithValue("@CustomerId", customerId);
        sqlCommand2.Parameters.AddWithValue("@CustomerId", customerId);

        _sqlConnection.Open();
        sqlCommand1.ExecuteScalar();
        sqlCommand2.ExecuteScalar();

        MessageBox.Show("删除用户成功！");
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
    finally
    {
        _sqlConnection.Close();
        ShowCustomers();
        customerList_SelectionChanged(null, null);
    }
}

2.实现添加
添加时，注意appointments的Id是取自customers的selectedvalue中

private void AddCustomer_Click(object sender, RoutedEventArgs e)
{
    try
    {
        var sql = "insert into Customers values(@name, @id, @address)";

        SqlCommand sqlCommand = new SqlCommand(sql, _sqlConnection);

        sqlCommand.Parameters.AddWithValue("@name", NameTextBox.Text);
        sqlCommand.Parameters.AddWithValue("@id", IdTextBox.Text);
        sqlCommand.Parameters.AddWithValue("@address", AddressTextBox.Text);

        _sqlConnection.Open();
        sqlCommand.ExecuteScalar();
        MessageBox.Show("添加用户信息成功！");
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
    finally
    {
        _sqlConnection.Close();
        ShowCustomers();

    }
}

private void AddAppointment_Click(object sender, RoutedEventArgs e)
{
    try
    {
        var sql = "insert into Appointments values(@date, @customerId)";

        SqlCommand sqlCommand = new SqlCommand(sql, _sqlConnection);

        sqlCommand.Parameters.AddWithValue("@date", AppointmentDatePicker.Text);
        sqlCommand.Parameters.AddWithValue("@customerId", customerList.SelectedValue);

        _sqlConnection.Open();
        sqlCommand.ExecuteScalar();
        MessageBox.Show("用户信息更新成功！");
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
    finally
    {
        _sqlConnection.Close();
        customerList_SelectionChanged(null, null);
    }
}

三、实现修改
实现修改，需要显示出项目数据，因此可以利用添加数据时的输入框来显示数据并完成修改，因此在 customerList_SelectionChanged函数中实现输入框显示数据

DataRowView selectItem = customerList.SelectedItem as DataRowView;
NameTextBox.Text = selectItem["Name"] as string;
IdTextBox.Text = selectItem["IdNumber"] as string;
AddressTextBox.Text = selectItem["Address"] as string;

那么就可以直接将输入框的数据接收传入修改

private void UpdateCustomer_Click(object sender, RoutedEventArgs e)
{
    try
    {
        var sql = "update Customers set Name=@name, IdNumber=@idNumber, Address=@address where Id=@customerId";


        SqlCommand sqlCommand = new SqlCommand(sql, _sqlConnection);

        sqlCommand.Parameters.AddWithValue("@name", NameTextBox.Text.Trim());//trim用来消除空格
        sqlCommand.Parameters.AddWithValue("@idNumber", IdTextBox.Text.Trim());
        sqlCommand.Parameters.AddWithValue("@address", AddressTextBox.Text.Trim());
        sqlCommand.Parameters.AddWithValue("@customerId", customerList.SelectedValue);

        _sqlConnection.Open();
        sqlCommand.ExecuteScalar();
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
    finally
    {
        _sqlConnection.Close();
        ShowCustomers();
    }
}

三、注意事项

由于对于数据库的操作是具有风险的，因此一定要将对外操作放进try,catch中，防止因为数据库的死机等意外造成系统的崩溃。
另外，一定要将数据库的关闭操作放置在finally中，防止出现内存泄漏的事故。