前面已经解释了DTO的作用，但实现领域对象与DTO之间的转换是一件复杂的事件，因此可以建立一个数据转换器实现此功能。
在平常的工作里，不太多会把"订单管理系统"做成SOA的模式，因为在分布式系统中，数据的格式与定义大多数由部门之间协定，其中包含明确的规则。但由于条件的局限，在这里还是想以订单管理为例子，希望可以带给你一定的帮助。例子如下：在购物车结账，页面会包含用户基本信息，当前订单信息，订单明细信息等多个部分。
要完成数据转换，首先可以根据页面建立DTO对象，在分布式系统中，通常会把DTO对象放在一个独立的命名空间里，在这个实例里面称之为Business.TransferObject。DTO对象更多时候是面向表现层的需求而建立，这里由于表现层页面所需要的只是单个用户，单张订单的数据，所以在OrderDTO对象里会包含了用户信息和订单资料，也存在订单详细列List<OrderItemDTO>。当然，DTO的设计可以随着需求而修改。
在SOA系统里，DTO是远程服务数据的载体，所以会把DTO附上可序列化特性，这此例子中会使用WCF的数据契约实现OrderDTO和OrderItemDTO。
如图，要实现数据转换，就应该建立数据转换器。在这里OperationAssembler就是一个数据转换器，它是数据转换的核心，它是领域对象与DTO之间实现转换的工具。要在多个对象之间实现数据转换实在是一件非常麻烦的事，所以我一直提倡注意DTO对象的兼容性，使单个DTO对象可以适用于多个外观层，以减少数据转换所带来的麻烦。
namespace Business.Service.ApplicationService
{
public class OperationAssembler
{
//把领域对象转换成DTO
public static OrderDTO GetOrderDTO(Order order,Person person)
{
OrderDTO orderDTO = new OrderDTO();
if (person != null)
{
orderDTO.EMail = person.EMail.GetString();
orderDTO.Address = person.Address.GetString();
orderDTO.Name = person.Name.GetString();
orderDTO.PersonID = person.ID;
orderDTO.Point = person.Point.GetInt();
orderDTO.Telephone = person.Telephone.GetString();
}
if (order != null)
{
orderDTO.PersonID = order.PersonID;
orderDTO.Count = order.Count.GetInt();
orderDTO.Delivery = order.Delivery.GetDateTime();
orderDTO.Favorable = order.Favorable.GetDouble();
orderDTO.Freightage = order.Freightage.GetDouble();
orderDTO.OrderID = order.ID;
orderDTO.OrderNumber = order.OrderNumber.GetString();
orderDTO.Price = order.Price.GetDouble();
orderDTO.TotalPrice = order.TotalPrice.GetDouble();
var orderItemList = order.OrderItem.ToList();
if (orderItemList.Count != 0)
{
var orderItemDTO = new List<OrderItemDTO>();
foreach (var orderItem in orderItemList)
orderItemDTO.Add(GetOrderItemDTO(orderItem));
orderDTO.OrderItemList = orderItemDTO;
}
}
return orderDTO;
}
public static OrderItemDTO GetOrderItemDTO(OrderItem orderItem)
{
OrderItemDTO orderItemDTO = new OrderItemDTO();
orderItemDTO.Count = orderItem.Count.GetInt();
orderItemDTO.Goods = orderItem.Goods.GetString();
orderItemDTO.OrderID = orderItem.OrderID;
orderItemDTO.OrderItemID = orderItem.ID;
orderItemDTO.Price = orderItem.Price.GetDouble();
return orderItemDTO;
}
//把DTO转换成多个对象
public static void SetOrder(OrderDTO orderDTO, out Person person, out Order order)
{
person = new Person();
person.EntityKey=new System.Data.EntityKey("BusinessContext.Person","ID",orderDTO.PersonID);
person.Address = orderDTO.Address;
person.EMail = orderDTO.EMail;
person.ID = orderDTO.PersonID;
person.Name = orderDTO.Name;
person.Point = orderDTO.Point;
person.Telephone = orderDTO.Telephone;
order = new Order();
order.EntityKey=new System.Data.EntityKey("BusinessContext.Order","ID",orderDTO.OrderID);
order.Count = orderDTO.Count;
if (orderDTO.Delivery.Year!=0001&&orderDTO.Delivery.Year!=9999)
order.Delivery = orderDTO.Delivery;
order.Favorable = orderDTO.Favorable;
order.Freightage = orderDTO.Freightage;
order.ID = orderDTO.OrderID;
order.OrderNumber = orderDTO.OrderNumber;
order.PersonID = orderDTO.PersonID;
order.Price = orderDTO.Price;
order.TotalPrice = orderDTO.TotalPrice;
var orderItemDTOList = orderDTO.OrderItemList;
if (orderItemDTOList.Count() != 0)
foreach (var orderItemDTO in orderItemDTOList)
order.OrderItem.Add(GetOrderItem(orderItemDTO));
}
public static OrderItem GetOrderItem(OrderItemDTO orderItemDTO)
{
OrderItem orderItem = new OrderItem();
orderItem.EntityKey = new System.Data.EntityKey("BusinessContext.OrderItem", "ID", orderItemDTO.OrderItemID);
orderItem.Count = orderItemDTO.Count;
orderItem.Goods = orderItemDTO.Goods;
orderItem.ID = orderItemDTO.OrderItemID;
orderItem.OrderID = orderItemDTO.OrderID;
orderItem.Price = orderItemDTO.Price;
return orderItem;
}
}
}
//数据传输对象 DTO
namespace Business.TransferObject
{
[DataContract]
public class OrderItemDTO
{
private int _orderItemID;
private int _orderID;
private string _goods;
private double _price;
private int _count;
[DataMember]
public int OrderItemID
{
get { return _orderItemID; }
set { _orderItemID = value; }
}
............
............
}
[DataContract]
public class OrderDTO
{
private int _personID;
private string _name;
private string _address;
private string _telephone;
private int _point;
private string _email;
private int _orderID;
private string _orderNumber;
private int _count;
private double _freightage;
private double _favorable;
private DateTime _delivery;
private double _price;
private double _totalPrice;
private IList<OrderItemDTO> _orderItemDTOList;
[DataMember]
public int PersonID
{
get{return this._personID;}
set{this._personID=value;}
}
..........
..........
}
}
通过数据转换器，可以顺利实现领域模型与DTO之间的转换，协调应用层服务的运行。
4. 应用层的发布
在开发SOA系统的时候，应用层的服务需要使用远程方法对外开放，在接收到请求的时候，它可以调用领域层服务获取运算结果，然后通过数据转换器OperationAssembler把运算结果转换成DTO，最后返还到表现层。在起初，我曾尝试对应每个应用层的对象建立一个远程接口，但经过多次重构以后，我觉得行程对象就是一个简单的对外接口，对象之间不存在什么逻辑关系。所以更简单的方法是使用外观模式，建立少数的几个远程服务类，把所有的应用层对象的方法都包含在内。
可以留意代码，OperationService包括了对Person模型和Order模型的所有操作。而且每个操作都只是简单地调用应用层服务 (ApplicationService) 获得计算结果，然后使用数据转换器 （OperationAssembler）转换数据，当中并不存在任何的业务逻辑。
namespace Business.Service.ApplicationService
{
[ServiceContract]
public interface IOperationService
{
[OperationContract]
int AddOrder(ref OrderDTO orderDTO);
[OperationContract]
int DeleteOrder(OrderDTO orderDTO);
[OperationContract]
int UpdateOrder(ref OrderDTO orderDTO);
[OperationContract]
IList<OrderDTO> GetOrderByPerson(int personID);
[OperationContract]
OrderDTO GetOrder(int orderID);
[OperationContract]
int AddPerson(ref OrderDTO orderDTO);
[OperationContract]
int UpdatePerson(ref OrderDTO orderDTO);
[OperationContract]
OrderDTO GetPerson(int personID);
[OperationContract]
IList<OrderDTO> GetPersonList();
[OperationContract]
OrderDTO Payment(int orderID);
}
public class OperationService:IOperationService
{
[OperationBehavior(TransactionScopeRequired = true, TransactionAutoComplete = true)]
public int AddOrder(ref OrderDTO orderDTO)
{
OrderService orderService = new OrderService();
Order order = GetOrder(orderDTO);
int n = orderService.AddOrder(order);
orderDTO = OperationAssembler.GetOrderDTO(order, null);
return n;
}
[OperationBehavior(TransactionScopeRequired = true, TransactionAutoComplete = true)]
public int DeleteOrder(OrderDTO orderDTO)
{
OrderService orderService = new OrderService();
return orderService.DeleteOrder(GetOrder(orderDTO));
}
[OperationBehavior(TransactionScopeRequired = true, TransactionAutoComplete = true)]
public int UpdateOrder(ref OrderDTO orderDTO)
{
OrderService orderService = new OrderService();
Order order = GetOrder(orderDTO);
int n = orderService.UpdateOrder(order);
orderDTO = OperationAssembler.GetOrderDTO(order, null);
return n;
}
..............
..............
}
}