我是EF的新手。因此，为了测试乐观并发，我使用了 EF 5、WPF 和一个已经创建的数据库。WPF 项目包含一个MainWindow通过TextBox1主键搜索客户、TextBox2编辑客户名称、textblock (txtLog)记录字段值和保存按钮的功能。为了模拟并发访问，SQL Server 2008我在 Management Studio 中执行查询“ update client set r01_nomcli = 'GGGGG' where r01_codcli = '4112010002';”，然后单击保存按钮。它工作正常并被DbUpdateConcurrencyException触发，但实体的原始值丢失并采用与当前值相同的值。这是因为“使用”块导致实体分离。为了解决这个问题，我必须在窗口的构造函数之前声明上下文并在“Window_Loaded” 事件是否还有其他方法？有助于了解使用 EF 的最佳实践以及如何使用 EF 5 构建可重用 DAL。谢谢。在代码下方：
public partial class OptimisticConcurrency : Window
{
//client is an entity
client _currentClient = null;
public OptimisticConcurrency()
{
InitializeComponent();
}
//**************************TextBox1 PreviewKeyDown Event Handler
private void TextBox_PreviewKeyDown_1(object sender, KeyEventArgs e)
{
if (e.Key == Key.Enter)
{
using (dbleaseEntities context = new dbleaseEntities())
{
_currentClient = context.client.Find(txtCode.Text);
if (_currentClient == null)
MessageBox.Show("Customer " + txtCode.Text + " not found.", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
else
this.DataContext = _currentClient;
}
}
}
//*****************Save Button Click Event Handler
private void Button_Click_2(object sender, RoutedEventArgs e)
{
using (dbleaseEntities context = new dbleaseEntities())
{
context.Configuration.ValidateOnSaveEnabled = false;
try
{
context.Entry(_currentClient).State = System.Data.EntityState.Modified;
context.SaveChanges();
MessageBox.Show("Success.", "Save", MessageBoxButton.OK, MessageBoxImage.Information);
}
catch (DbEntityValidationException ex)
{
string ss = "";
foreach (var error in ex.EntityValidationErrors)
ss = string.Join(Environment.NewLine, error.ValidationErrors.Select(v => v.ErrorMessage));
MessageBox.Show(ss, "Error", MessageBoxButton.OK, MessageBoxImage.Error);
}
catch (DbUpdateConcurrencyException ex)
{
string StrValues= "";
DbPropertyValues ov = ex.Entries.Single().OriginalValues;
DbPropertyValues cv = ex.Entries.Single().CurrentValues;
DbPropertyValues dv = ex.Entries.Single().GetDatabaseValues();
StrValues= "Original value : " + ov["r01_nomcli"] + Environment.NewLine +
"Current value : " + cv["r01_nomcli"] + Environment.NewLine +
"Database value : " + dv["r01_nomcli"];
txtLog.Text = StrValues
}
}
}