对数据访问层的重构(及重构中Perl的应用)
以前上学的时候,听到“一个学生在毕业后刚刚开始编程的头几年中,写出的代码多半是垃圾”这样的说法,均不屑一顾。现在工作一年多了,越发感觉自己代码中疏漏处甚多,故近来常做亡羊补牢的重构之举。拿自己4个月前写的数据访问层来说,这个层位于整个系统的最底端,根据传入的sql语句进行查询和更新操作。就拿查询来说吧,我当时觉得很简单,写出来的方法是这样的:
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而此方法都是这样被我调用的:
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有心的朋友很容易就能看出,如此的代码是非常脆弱的,根本无法应付查询字符串中出现特殊字符的情况(单引号,百分号等)。程序容错性差不说,还容易遭到sql注入的攻击。另外,对于sql操作可能抛出的异常,这里捕获之后就跳转到出错页的方式也是很糟糕的;因为这段底层代码,除了会被页面调用以外,还会被其他一些不是由客户端请求引发的功能所调用(如部署到服务器上的windows服务,处理复杂任务的专用工作线程等),在这些调用环境里HttpContext.Current是没有意义的。实际上,在这种底层的代码里,只能对异常作必要的处理,至于究竟是跳转到一个友好的错误提示界面,还是写入错误日志,应当交给更高层的代码去决定。
对这部分的重构其实很简单,那就是在进行查询的时候,对于所有参数都以SqlParameter进行封装。重构中新增了方法PrepareCommand,用来得到我们需要的SqlCommand对象。对ExecuteQuery的重构如下:
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上面重构的是ExecuteQuery方法的定义部分,这其实只是重构的开始,因为现有代码中充满了类似代码段2那样的方法调用,都需要改成如下的形式:
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比照一下上面贴出的代码段2和代码段4,它们之间的差异就是我很希望自己能通过正则表达式跨越的鸿沟(一个一个手工去改的话实在太累了,一百多处啊,呵呵)。需要注意的是,查询语句中可能出现的参数个数是不定的,每个文件中可能包含的方法调用的数量也是不定的。本想写一个C#的console小程序来完成这个批量操作,但又总觉得杀鸡用牛刀,后来写了一个简单的perl脚本,利用perl强大的文本处理能力,很容易就实现了这个功能。脚本代码如下:
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********:该做什么就做什么,不该做什么就不做什么?还是不该做什么可以不做什么?