public interface DataAccess

     {

         DatabaseType DatabaseType{get;}                  //数据库类型

          IDbConnection DbConnection{get;}  //得到数据库连接

         void Open();                    //打开数据库连接

         void Close();                   //关闭数据库连接

         IDbTransaction BeginTransaction();              //开始一个事务

         int ExecuteNonQuery(string commandText);       //执行Sql语句

         DataSet ExecuteDataset(string commandText);//执行Sql，返回DataSet

}

     public sealed class MSSqlDataAccess : AbstractDataAccess

     {

         ……//具体实现代码。

     }

     public class OleDbDataAccess : AbstractDataAccess

     {

          ……//具体实现代码。

     }

     public class OracleDataAccess : AbstractDataAccess

     {

         ……//具体实现代码。

     }

     public sealed class DataAccessFactory

     {

         private DataAccessFactory(){}

         private static PersistenceProperty defaultPersistenceProperty;

         public static PersistenceProperty DefaultPersistenceProperty

         {

              get{return defaultPersistenceProperty;}

              set{defaultPersistenceProperty=value;}

         }

         public static DataAccess CreateDataAccess(PersistenceProperty pp)

         {

              DataAccess dataAccess;

              switch(pp.DatabaseType)

              {

                   case(DatabaseType.MSSQLServer):

                       dataAccess = new MSSqlDataAccess(pp.ConnectionString);

                       break;

                   case(DatabaseType.Oracle):

                       dataAccess = new OracleDataAccess(pp.ConnectionString);

                       break;

                   case(DatabaseType.OleDBSupported):

                       dataAccess = new OleDbDataAccess(pp.ConnectionString);

                       break;

                   default:

                       dataAccess=new MSSqlDataAccess(pp.ConnectionString);

                       break;

              }

              return dataAccess;

         }

         public static DataAccess CreateDataAccess()

         {

              return CreateDataAccess(defaultPersistenceProperty);

         }

     }

PersistenceProperty pp = new PersistenceProperty();

pp.ConnectionString = "server=127.0.0.1;uid=sa;pwd=;database=Northwind;";

pp.DatabaseType = DatabaseType. MSSQLServer;

pp.UserID = “sa”;

pp.Password = “”;

DataAccess db= DataAccessFactory.CreateDataAccess(pp)

db.Open();

……//db.需要的操作

db.Close();

或者，如果事先设定了DataAccessFactory的DefaultPersistenceProperty属性，可以直接使用

DataAccess db= DataAccessFactory.CreateDataAccess()

方法创建DataAccess实例。