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"/>
1using System.Reflection;
2using 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.
DataProviders
1//------------------------------------------------------------------------------
2// <copyright company="Telligent Systems">
3// Copyright (c) Telligent Systems Corporation. All rights reserved.
4// </copyright>
5//------------------------------------------------------------------------------
6
7using System;
8using System.Configuration;
9using System.IO;
10using System.Reflection;
11using System.Web;
12using CommunityServer.Configuration;
13
14namespace CommunityServer.Components
15{
16 /**//// <summary>
17 /// DataProviders is responible for loading and managing the various CS DataProviders
18 /// </summary>
19 public sealed class DataProviders
20 {
21 /**//// <summary>
22 /// This class can not be instantiated
23 /// </summary>
24 private DataProviders()
25 {
26 }
27
28 private static void GetDataStoreParameters(Provider dataProvider, out string connectionString, out string databaseOwner)
29 {
30 databaseOwner = dataProvider.Attributes["databaseOwner"];
31 if(databaseOwner == null || databaseOwner.Trim().Length == 0)
32 databaseOwner = ConfigurationSettings.AppSettings[dataProvider.Attributes["databaseOwnerStringName"]];
33
34 connectionString = dataProvider.Attributes["connectionString"];
35 if(connectionString == null || connectionString.Trim().Length == 0)
36 connectionString = ConfigurationSettings.AppSettings[dataProvider.Attributes["connectionStringName"]];
37 }
38
39 /**//// <summary>
40 /// Creates an instance of the provider using Activator. This instance should be
41 /// cached since it is an expesivie operation
42 /// </summary>
43 public static object CreateInstance(Provider dataProvider)
44 {
45 //Find the current attributes
46 string connectionString = null; //dataProvider.Attributes["connectionString"];
47 string databaseOwner = null;// dataProvider.Attributes["databaseOwner"];
48
49 GetDataStoreParameters(dataProvider, out connectionString, out databaseOwner);
50
51 //Get the type
52 Type type = Type.GetType(dataProvider.Type);
53
54 object newObject = null;
55 if(type != null)
56 {
57 newObject = Activator.CreateInstance(type,new object[]{databaseOwner,connectionString});
58 }
59
60 if(newObject == null) //If we can not create an instance, throw an exception
61 ProviderException(dataProvider.Name);
62
63 return newObject;
64 }
65
66 /**//// <summary>
67 /// Creates and Caches the ConstructorInfo for the specified provider.
68 /// </summary>
69 public static ConstructorInfo CreateConstructorInfo (Provider dataProvider)
70 {
71
72 // The assembly should be in \bin or GAC, so we simply need
73 // to get an instance of the type
74 //
75 CSConfiguration config = CSConfiguration.GetConfig();
76 ConstructorInfo providerCnstr = null;
77 try
78 {
79 //string providerTypeName = ((Provider) config.Providers[providerName]).Type;
80 Type type = Type.GetType( dataProvider.Type );
81
82 // Insert the type into the cache
83 //
84 Type[] paramTypes = new Type[2];
85 paramTypes[0] = typeof(string);
86 paramTypes[1] = typeof(string);
87
88 providerCnstr = type.GetConstructor(paramTypes);
89
90 }
91 catch
92 {
93 ProviderException(dataProvider.Name);
94 }
95
96 if(providerCnstr == null)
97 ProviderException(dataProvider.Name);
98
99 return providerCnstr;
100 }
101
102 /**//// <summary>
103 /// Creates an instance of the specified provider using the Cached
104 /// ConstructorInfo from CreateConstructorInfo
105 /// </summary>
106 public static object Invoke(Provider dataProvider)
107 {
108 object[] paramArray = new object[2];
109
110
111 string dbOwner = null;
112 string connstring = null;
113
114 GetDataStoreParameters(dataProvider, out connstring, out dbOwner);
115
116 paramArray[0] = dbOwner;
117 paramArray[1] = connstring;
118
119 return CreateConstructorInfo(dataProvider).Invoke(paramArray);
120 }
121
122 Exception#region Exception
123 private static void ProviderException(string providerName)
124 {
125 CSConfiguration config = CSConfiguration.GetConfig();
126 HttpContext context = HttpContext.Current;
127 if (context != null)
128 {
129
130 // We can't load the dataprovider
131 //
132 StreamReader reader = new StreamReader( context.Server.MapPath("~/Languages/" + config.DefaultLanguage + "/errors/DataProvider.htm") );
133 string html = reader.ReadToEnd();
134 reader.Close();
135
136 html = html.Replace("[DATAPROVIDERCLASS]", providerName);
137 html = html.Replace("[DATAPROVIDERASSEMBLY]", providerName);
138 context.Response.Write(html);
139 context.Response.End();
140 }
141 else
142 {
143 throw new CSException(CSExceptionType.DataProvider, "Unable to load " + providerName);
144 }
145 }
146 #endregion
147 }
148}
文章是越写越不知道写些什么?CS有很多人研究他,应该会有关于这样的文章,不多说了,呵呵.