下面我们来看看provider的配制文件:
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从上面可以看到,provider主要包括两个配制,一个是name:用于搜索用的唯一provider名称;type:工作类的程序集和类,一定要按照"类,程序集"的顺序,不然会出错的哦,不信你试试!当然还有其它配制,在CS中可以将其它配制存在一个NameValueCollection中,这样就可以随便扩展而不要写他的实体类了,这也是值得我们学习的地方啊。
知道了配置文件,我们可以从CSConfiguration.cs文件中找到Provider的实体类,通过CSConfiguration类将其读取并缓存,这样能提高效率。关于怎样读取,我想回用XML的人都懂得,这里就不多说了,下面来看看代码。
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Nme就是上面所说的配置节点中的name属性;Type就是type属性,将其他的如ConnectionString等保存在Attributes中,我们可以通过key&value来读取。到这里我们已经读取了provider配置,但要实现provider还需要通过反射技术,在DataProviders可以看到,这个类主要用于数据库的扩展类,一些非数据库的类大多用SingletonProviderHelper来实现,原理都差不多,主要DataProviders通过查找最匹配的具有(string connectionString,string dataOwrer)来对其实例化,在CSlReWriter类中就可以看到用SingletonProviderHelper来对其虚函数进行实例化。
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public sealed class DataProviders
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{
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/// <summary>
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/// This class can not be instantiated
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/// </summary>
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private DataProviders()
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{
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}
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private static void GetDataStoreParameters(Provider dataProvider, out string connectionString, out string databaseOwner)
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{
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databaseOwner = dataProvider.Attributes["databaseOwner"];
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if(databaseOwner == null || databaseOwner.Trim().Length == 0)
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databaseOwner = ConfigurationSettings.AppSettings[dataProvider.Attributes["databaseOwnerStringName"]];
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connectionString = dataProvider.Attributes["connectionString"];
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if(connectionString == null || connectionString.Trim().Length == 0)
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connectionString = ConfigurationSettings.AppSettings[dataProvider.Attributes["connectionStringName"]];
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}
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/// <summary>
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/// Creates an instance of the provider using Activator. This instance should be
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/// cached since it is an expesivie operation
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/// </summary>
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public static object CreateInstance(Provider dataProvider)
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{
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//Find the current attributes
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string connectionString = null; //dataProvider.Attributes["connectionString"];
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string databaseOwner = null;// dataProvider.Attributes["databaseOwner"];
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GetDataStoreParameters(dataProvider, out connectionString, out databaseOwner);
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//Get the type
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Type type = Type.GetType(dataProvider.Type);
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object newObject = null;
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if(type != null)
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{
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newObject = Activator.CreateInstance(type,new object[]{databaseOwner,connectionString});
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}
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if(newObject == null) //If we can not create an instance, throw an exception
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ProviderException(dataProvider.Name);
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return newObject;
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}
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/// <summary>
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/// Creates and Caches the ConstructorInfo for the specified provider.
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/// </summary>
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public static ConstructorInfo CreateConstructorInfo (Provider dataProvider)
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{
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// The assembly should be in \bin or GAC, so we simply need
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// to get an instance of the type
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//
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CSConfiguration config = CSConfiguration.GetConfig();
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ConstructorInfo providerCnstr = null;
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try
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{
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//string providerTypeName = ((Provider) config.Providers[providerName]).Type;
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Type type = Type.GetType( dataProvider.Type );
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// Insert the type into the cache
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//
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Type[] paramTypes = new Type[2];
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paramTypes[0] = typeof(string);
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paramTypes[1] = typeof(string);
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providerCnstr = type.GetConstructor(paramTypes);
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}
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catch
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{
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ProviderException(dataProvider.Name);
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}
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if(providerCnstr == null)
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ProviderException(dataProvider.Name);
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return providerCnstr;
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}
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/// <summary>
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/// Creates an instance of the specified provider using the Cached
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/// ConstructorInfo from CreateConstructorInfo
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/// </summary>
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public static object Invoke(Provider dataProvider)
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{
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object[] paramArray = new object[2];
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string dbOwner = null;
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string connstring = null;
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GetDataStoreParameters(dataProvider, out connstring, out dbOwner);
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paramArray[0] = dbOwner;
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paramArray[1] = connstring;
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return CreateConstructorInfo(dataProvider).Invoke(paramArray);
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}
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通过Type.GetType()来进行类的反射,当然我们需要对其进行实例化才能调用abstract class中的方法和属性,这就要用到Activator.CreateInstance(type,new object[]{databaseOwner,connectionString}),这个方法对类进行了实例化,当然实例化这个类的构造函数中的参数为(databaseOwner,connectionString);当查找到这个构造函数进行实例化时也将DataProvider中所得到的databaseOwner,connectionString两个变量的值传递给了参数。
OK这样就完成了整个实现过程,如果有不对的地方请批评指正!