动软的DBHelper类-请高手帮忙解释下..

Question

/// 
        /// 检测一个记录是否存在(SQL语句方式)
        /// 
         public static bool Exists(string strSql)
         {
            Database db = DatabaseFactory.CreateDatabase();
            DbCommand dbCommand = db.GetSqlStringCommand(strSql);
            object obj = db.ExecuteScalar(dbCommand);
              int cmdresult;
              if ((Object.Equals(obj, null)) || (Object.Equals(obj, System.DBNull.Value)))
              {
                   cmdresult = 0;
              }
              else
              {
                   cmdresult = int.Parse(obj.ToString());
              }
              if (cmdresult == 0)
              {
                   return false;
              }
              else
              {
                   return true;
              }
         }

Answer 1

执行一条查询语句，然后检查查询后的结果，如果为null或DBNull（表示不存在的值），返回false。否则返回false。比如，select * from A where ID=99，不存在该记录返回false

Answer 2

Database db = DatabaseFactory.CreateDatabase();//创建连接
 执行SQK语句
获取获取值

Answer 3

Database db = DatabaseFactory.CreateDatabase();
DbCommand dbCommand = db.GetSqlStringCommand(strSql);
只需要解释这两句就好了  

Answer 4

Database db = DatabaseFactory.CreateDatabase()工厂模式创建连接和操作类