运用反射实现多层和多数据库开发
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现在很多项目都须要为将来的扩展考虑,当然数据库也是一个很重我要的方面,扩展自己的Provider,这就需要反射技术,虽然会对性能有所影响,但是性价比还是很高的哦,从PetShop和CommunityServer都可以看到反射技术啦,也可以说反射是最基本的啦,呵呵!他的老家是在System.Reflection,当我们要开工时首先就是要把他抓出来. 要实现这一功能我们当然要知道Provider的程序集,和工作的类名了,在多层架够中才能让逻辑和数据进行沟通,这样也方便团队开发的协条款发展,我们通过PetShop和CommunityServer两个例子来说明一下. 我们先看看PetShop的反射技术,在配制文件中发现如下配制:
<!-- Pet Shop DAL configuration settings --> < add key ="WebDAL" value ="PetShop.SQLServerDAL" /> < add key ="OrdersDAL" value ="PetShop.SQLServerDAL" /> < add key ="ProfileDAL" value ="PetShop.SQLProfileDAL" /> 1 using System.Reflection; 2 using System.Configuration; 3 4 
namespace PetShop.DALFactory { 5 
6 
/// <summary> 7 /// This class is implemented following the Abstract Factory pattern to create the DAL implementation 8 /// specified from the configuration file 9 
/// </summary> 10 public sealed class DataAccess { 11 12 // Look up the DAL implementation we should be using 13 private static readonly string path = ConfigurationManager.AppSettings[ " WebDAL " ]; 14 private static readonly string orderPath = ConfigurationManager.AppSettings[ " OrdersDAL " ]; 15 16 private DataAccess() { } 17 18 public static PetShop.IDAL.ICategory CreateCategory() { 19 string className = path + " .Category " ; 20 return (PetShop.IDAL.ICategory)Assembly.Load(path).CreateInstance(className); 21 } 22 23 public static PetShop.IDAL.IInventory CreateInventory() { 24 string className = path + " .Inventory " ; 25 return (PetShop.IDAL.IInventory)Assembly.Load(path).CreateInstance(className); 26 } 27 28 public static PetShop.IDAL.IItem CreateItem() { 29 string className = path + " .Item " ; 30 return (PetShop.IDAL.IItem)Assembly.Load(path).CreateInstance(className); 31 } 32 33 public static PetShop.IDAL.IOrder CreateOrder() { 34 string className = orderPath + " .Order " ; 35 return (PetShop.IDAL.IOrder)Assembly.Load(orderPath).CreateInstance(className); 36 } 37 38 public static PetShop.IDAL.IProduct CreateProduct() { 39 string className = path + " .Product " ; 40 return (PetShop.IDAL.IProduct)Assembly.Load(path).CreateInstance(className); 41 } 42 43 } 44 
}
其中(PetShop.IDAL.IProduct)Assembly.Load(path).CreateInstance(className);就是将类进行反射,首先要载入程序集,然后再创进类实例,通过静态方法就可以直接调用接口的方法等,从而实现了继承接口的类的反射,同时也方便表现层的数据传输. 下面我们来看一下CommunityServer是怎么实现的,CS是一个大象极别的项目,所以他有很自己扩展Provider,那怎么样才能让他们工作呢?其实原理和上述的反射方法差不多,只不过CS用的是Object.GetTyp()而达到这项功能.当我第一次看到时,还一直为怎样传输ConnectionString&DataOwner而不解,后来打开源数据看了一下各个方法的注解后才理解. CS从自定的配制文件中读取Provider节点并缓存,这在CSConfiguration类中可以发现,在DataProviders类中就实现反射,通过能构造函数的反射查找最匹配的构造函数对类进行实例化,当然当他们遇到有ConnectionString&DataOwner两参数的构造函数时,就对其进行实例化,从而达到对他们值的传输. using System.Reflection; 2 using System.Configuration; 3 4 namespace PetShop.DALFactory { 5 6 /// <summary> 7 /// This class is implemented following the Abstract Factory pattern to create the DAL implementation 8 /// specified from the configuration file 9 /// </summary> 10 public sealed class DataAccess { 11 12 // Look up the DAL implementation we should be using 13 private static readonly string path = ConfigurationManager.AppSettings[ " WebDAL " ]; 14 private static readonly string orderPath = ConfigurationManager.AppSettings[ " OrdersDAL " ]; 15 16 private DataAccess() { } 17 18 public static PetShop.IDAL.ICategory CreateCategory() { 19 string className = path + " .Category " ; 20 return (PetShop.IDAL.ICategory)Assembly.Load(path).CreateInstance(className); 21 } 22 23 public static PetShop.IDAL.IInventory CreateInventory() { 24 string className = path + " .Inventory " ; 25 return (PetShop.IDAL.IInventory)Assembly.Load(path).CreateInstance(className); 26 } 27 28 public static PetShop.IDAL.IItem CreateItem() { 29 string className = path + " .Item " ; 30 return (PetShop.IDAL.IItem)Assembly.Load(path).CreateInstance(className); 31 } 32 33 public static PetShop.IDAL.IOrder CreateOrder() { 34 string className = orderPath + " .Order " ; 35 return (PetShop.IDAL.IOrder)Assembly.Load(orderPath).CreateInstance(className); 36 } 37 38 public static PetShop.IDAL.IProduct CreateProduct() { 39 string className = path + " .Product " ; 40 return (PetShop.IDAL.IProduct)Assembly.Load(path).CreateInstance(className); 41 } 42 43 } 44 } 
DataProviders 本文转自网魂小兵博客园博客，原文链接：http://www.cnblogs.com/xdotnet/archive/2006/10/11/use_system_reflection_easy.html，如需转载请自行联系原作者
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