原始列表与编辑的对象列表;如何使用 linq 查找已编辑的项目

Question

我有一个实现IEquatable接口的OrderDto类。 我有一个从数据库中检索的订单列表，这些订单作为 OrderDto 对象。 此列表由最终用户编辑...添加新对象;删除现有对象;编辑现有对象。 我需要确定以下内容：

1. 列表中的新对象;
2. 列表中已删除的对象;
3. 列表中已编辑的对象;

我已经注释了以下代码来讨论这三个目标。 前两项是微不足道的，但我列表中的第三项非常烦人！ 我似乎无法使用 linq 创建它。 我希望你能在正确的方向上给我一个推动。 有关详细信息，请参阅以下代码。

感谢您的帮助！话筒

// Get the original list of OrderDtos before the user did anything.
var entityOrders = Mapper.Map<IList<OrderEntity>, IList<OrderDto>>(entity.Orders.ToList());  
// dto.Orders is a parameter that is being used in this code.  It is the list of OrderDto
// objects that the user has modified: Insert, edit, delete.
// Works properly to locate items that were deleted.          
var deletedOrders = entityOrders.Except(dto.Orders);
// Works properly to locate items that were added.
var addedOrders = dto.Orders.Except(entityOrders);
// Determine the list of order objects less new orders in the list.
// The user has already deleted objects, so we don't have to worry
// about them.  This list will contain only items that MAY have 
// been edited.
var potentialChanges = dto.Orders.Except(addedOrders);
// ARGGG!  I cannot seem to get this one to work properly!  As you can see in the 
// definition of the OrderDto, it implements the IEquatable interface.  So, it 
// should be very easy to determine which items in the dto.Orders list have been
// edited as opposed to the original version in the entityOrders list.  What I 
// would like to have is a list of all the OrderDto objects in the dto.Orders list
// that have been modified.  Since OrderDto implements IEquatable, we should be able
// to compare OrderDto objects directly, but I have not been able get it to work.
// Please helP! :)
var changedOrders =
   from dtoOrder in potentialChanges
   let entityOrder = entityOrders.First(x => x.OrderId == dtoOrder.OrderId)
   where entityOrder != null && !dtoOrder.Equals(entityOrder)
   select dtoOrder;

以下是 OrderDto 类的定义...

public class OrderDto : IEquatable<OrderDto>
{
    public long OrderId { get; set; }
    public string DisplayAs { get; set; }
    #region IEquatable
    public override int GetHashCode()
    {
        // Populate with all fields so
        // we can detect when an entity
        // has been edited.
        return 
        (
            (int) OrderId ^ 
            DisplayAs.GetHashCode()
        );
    }
    public override bool Equals(object other)
    {
        return this.Equals(other as OrderDto);
    }
    public bool Equals(OrderDto other)
    {
        // Populate with all fields so
        // we can detect when an entity
        // has been edited.
        return 
        (
            other != null &&
            other.OrderId == this.OrderId &&
            other.DisplayAs == this.DisplayAs 
        );
    } 
    #endregion
}

Answer 1

最简单的方法可能是包含 State 属性，例如值 New, Saved, Loaded, Modified 。您还可以添加IsDeleted属性。

然后，实现设置为引发PropertyChanged事件的每个属性，并实现自动将 State 属性设置为 Modified 的事件处理程序。

稍后您可以轻松查询：

var modified = entityOrders.Where(x => x.State == EntityState.Modified);

这种方法的优点是非常刻意的，即，你是明确的，代码是可读的，而不是试图变得困难（并且编写太多和太复杂的代码）。

以同样的方式，您可以实现一个 Delete（） 方法，该方法只是将实体标记为已删除，并将所有已删除的实体查询为：

var deleted = entityOrders.Where(x => x.IsDeleted);

或

// ignore objects that were created, then deleted, without saving
var deleted = entityOrders.Where(x => x.IsDeleted && x.State != x.New); 

以及所有有效数据：

var data = entityOrders.Where(x => !x.IsDeleted);