实体框架5.0处理乐观并发异常？

Question

在context.SaveChanges()其中一个例外情况下处理几个潜在的异常时OptimisticConcurrency.有关此问题的Microsoft文档,请访问http://msdn.microsoft.com/en-us/library/bb399228.aspx,对于EF 4.x进行了讨论.

try
{
    // Try to save changes, which may cause a conflict.
    int num = context.SaveChanges();
    Console.WriteLine("No conflicts. " +
        num.ToString() + " updates saved.");
}
catch (OptimisticConcurrencyException)
{
    // Resolve the concurrency conflict by refreshing the 
    // object context before re-saving changes. 
    context.Refresh(RefreshMode.ClientWins, orders);

    // Save changes.
    context.SaveChanges();
    Console.WriteLine("OptimisticConcurrencyException "
    + "handled and changes saved");
}

...但是在EF 5.0(RC)上,这似乎不起作用,因为Refresh()我的EF5,代码优先,DbContext派生context类上不存在.

我确实看到了context.Entry(context.SalesOrderHeaders).Reload();- 但这似乎是一个直接从db重新加载而不是刷新/合并(与策略客户端获胜).

任何想法如何处理EF5中的乐观并发异常？实际上甚至在SaveChanges()中关于异常处理的一般指针都会很好

谢谢

Answer 1

在DbContext API中如何解决并发异常的方法重新加载原始实体:

catch (DbUpdateConcurrencyException ex)
{
    // Get failed entry
    var entry = ex.Entries.Single(...);
    // Overwrite original values with values from database but don't
    // touch current values where changes are held
    entry.OriginalValues.SetValues(entry.GetDatabaseValues());
}

您还应该能够使用上面提到的代码,但是您必须ObjectContext从您的DbContext实例中获取实例(它只是一个包装器ObjectContext).

catch (DbUpdateConcurrencyException ex)
{
    var objContext = ((IObjectContextAdapter)context).ObjectContext;
    // Get failed entry
    var entry = ex.Entries.Single(...);
    // Now call refresh on ObjectContext
    objContext.Refresh(RefreshMode.ClientWins, entry.Entity);        
}

你甚至可以尝试:

objContext.Refresh(RefreshMode.ClientWins, ex.Entries.Select(e => e.Entity));