微软企业库源码解析——DAAB（一）DatabaseFactory

首先从最常用的数据获取块开始下手。

我们每次使用数据获取块首先做的就是得到一个Database

Database db = DatabaseFactory.CreateDatabase()

我们首先从DatabaseFactory着手

从名字上即可以猜测，DatabaseFactory是工厂模式的应用，用来创建一个恰当的Database。我们知道DAAB是兼容多种数据库的（MSSQL，Oracle等），因此所创建的Database应该是特异化的Database，比如SqlDatabase，从源代码的结构上看也是这样的。

再来看DatabaseFactory的代码

public static class DatabaseFactory

DatabaseFactory是一个静态类，其中只含有静态方法

public static Database CreateDatabase();public static Database CreateDatabase(string name);private static void TryLogConfigurationError(ConfigurationErrorsException configurationException, string instanceName)

我们关注的是CreateDatabase方法，这两个方法差不多，不过一个是得到默认Database一个是得到指定的Database

1: public static Database CreateDatabase() 2: { 3: try 4: { 5: DatabaseProviderFactory factory = new DatabaseProviderFactory(ConfigurationSourceFactory.Create()); 6: return factory.CreateDefault(); 7: } 8: catch (ConfigurationErrorsException configurationException) 9: { 10: TryLogConfigurationError(configurationException, "default"); 11:  12: throw; 13: } 14: }

从上面的代码我们可以发现DatabaseFactory是从DatabaseProviderFactory获得了Database并返回的，同时尝试把发生的错误记录下来，然后异常又被再次抛出了。

对于异常的处理并不是我们关心的，我们继续去看DatabaseProviderFactory。

1: public class DatabaseProviderFactory : NameTypeFactoryBase<Database> 2: { 3: /// <summary> 4: /// <para>Initializes a new instance of the <see cref="DatabaseProviderFactory"/> class 5: /// with the default configuration source.</para> 6: /// </summary> 7: protected DatabaseProviderFactory() 8: : base() 9: { 10: } 11:  12: /// <summary> 13: /// <para>Initializes a new instance of the <see cref="DatabaseProviderFactory"/> class 14: /// with the given configuration source.</para> 15: /// </summary> 16: /// <param name="configurationSource">The source for configuration information.</param> 17: public DatabaseProviderFactory(IConfigurationSource configurationSource) 18: : base(configurationSource) 19: {} 20:  21: }

可以知道，DatabaseFactory用ConfigurationSourceFactory创建的一个配置源装配了DatabaseProviderFactory。看来重点在NameTypeFactoryBase上。

我们来看NameTypeFactoryBase。

1: /// <summary> 2: /// Base class for instance factories. 3: /// </summary> 4: /// <remarks> 5: /// This class is used to create instances of types compatible with <typeparamref name="T"/> described 6: /// by a configuration source. 7: /// </remarks> 8: public class NameTypeFactoryBase<T> 9: { 10: private IConfigurationSource configurationSource; 11:  12: /// <summary> 13: /// Initializes a new instance of the <see cref="NameTypeFactoryBase{T}"/> class with the default configuration source. 14: /// </summary> 15: protected NameTypeFactoryBase() 16: : this(ConfigurationSourceFactory.Create()) 17: { 18: } 19:  20: /// <summary> 21: /// Initializes a new instance of the <see cref="NameTypeFactoryBase{T}"/> class with a configuration source. 22: /// </summary> 23: /// <param name="configurationSource">The configuration source to use.</param> 24: protected NameTypeFactoryBase(IConfigurationSource configurationSource) 25: { 26: this.configurationSource = configurationSource; 27: } 28:  29: /// <summary> 30: /// Returns a new instance of <typeparamref name="T"/> based on the default instance configuration. 31: /// </summary> 32: /// <returns> 33: /// A new instance of <typeparamref name="T"/>. 34: /// </returns> 35: public T CreateDefault() 36: { 37: return EnterpriseLibraryFactory.BuildUp<T>(configurationSource); 38: } 39:  40: /// <summary> 41: /// Returns an new instance of <typeparamref name="T"/> based on the configuration for <paramref name="name"/>. 42: /// </summary> 43: /// <param name="name">The name of the required instance.</param> 44: /// <returns> 45: /// A new instance of <typeparamref name="T"/>. 46: /// </returns> 47: public T Create(string name) 48: { 49: return EnterpriseLibraryFactory.BuildUp<T>(name, configurationSource); 50: } 51: }

回忆DatabaseFactory类，在创建了一个DatabaseProviderFactory后即调用了其Create或CreateDefault方法，这两个方法都是由NameTypeFactoryBase<Database>继承的。从这里可以看出，NameTypeFactoryBase用EnterpriseLibraryFactory从配置源读取配置并装配了Database类。

我们继续挖掘到EnterpriseLibraryFactory类。

public static class EnterpriseLibraryFactory

这也是一个静态类。这个类代码比较多，我就拣几段重要的贴上来。

1: static EnterpriseLibraryFactory() 2: { 3: builder = new Builder(); 4: StagedStrategyChain<BuilderStage> stagedStrategyChain = new StagedStrategyChain<BuilderStage>(); 5: stagedStrategyChain.AddNew<ConfigurationNameMappingStrategy>(BuilderStage.PreCreation); 6: stagedStrategyChain.AddNew<LocatorLookupStrategy>(BuilderStage.PreCreation); 7: stagedStrategyChain.AddNew<ConfiguredObjectStrategy>(BuilderStage.PreCreation); 8: stagedStrategyChain.AddNew<InstrumentationStrategy>(BuilderStage.PostInitialization); 9: strategyChain = stagedStrategyChain.MakeStrategyChain(); 10: } 1: public static T BuildUp<T>(IConfigurationSource configurationSource) 2: { 3: return BuildUp<T>(null, null, configurationSource); 4: } 5:  6: public static T BuildUp<T>(IReadWriteLocator locator, 7: ILifetimeContainer lifetimeContainer, 8: IConfigurationSource configurationSource) 9: { 10: if (configurationSource == null) 11: throw new ArgumentNullException("configurationSource"); 12:  13: try 14: { 15: return GetObjectBuilder() 16: .BuildUp<T>(locator, 17: lifetimeContainer, 18: GetPolicies(configurationSource), 19: strategyChain, 20: NamedTypeBuildKey.Make<T>(), 21: null); 22:  23: } 24: catch (BuildFailedException e) 25: { 26: // look for the wrapped ConfigurationErrorsException, if any, and throw it 27: ConfigurationErrorsException cee = GetConfigurationErrorsException(e); 28: if (cee != null) 29: { 30: throw cee; 31: } 32:  33: // unknown exception, bubble it up 34: throw; 35: } 36: }

1: private static PolicyList GetPolicies(IConfigurationSource configurationSource) 2: { 3: PolicyList policyList = new PolicyList(); 4: policyList.Set<IConfigurationObjectPolicy>(new ConfigurationObjectPolicy(configurationSource), 5: typeof(IConfigurationSource)); 6: policyList.Set<IReflectionCachePolicy>(new ReflectionCachePolicy(reflectionCache), 7: typeof(IReflectionCachePolicy)); 8:  9: return policyList; 10: } 11:  12: private static IBuilder GetObjectBuilder() 13: { 14: return builder; 15: } 16:  17: private static IConfigurationSource ConfigurationSource 18: { 19: get { return ConfigurationSourceFactory.Create(); } 20: }

熟悉Unity的朋友应该能猜到，大概是按照StrategyChain对Database进行了装配。

现在关键就在builder上了，可是Builder是ObjectBuilder2中的类，没有源码。

今天的工作先到这里了。

转载于:https://www.cnblogs.com/HCOONa/archive/2009/07/13/1522675.html

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