项目和新需求：

我们有一个PHP写的webmail系统，有一个mail_list.php用于展现用户的邮件列表这个页面支持folderId参数（因为邮件是存在不同的文件夹下的）由于邮件太多所以支持翻页。现在需要在系统里增加标签。细化下来：需要在原有的邮件列表里增加标签列，和支持tagid检索出一个邮件列表（列表里也增加标签列）

代码和新需求

mail_list.php调用GetMailList函数，这个函数传入文件夹ID,页码，页大小，得到HTML TABLE和导航链接

GetMailList用T_Page类得到请求的一页数据再处理为HTML表格

虽然T_Page只支持单表查询，但是在整个系统里还是被广泛使用

因为动T_Page还是有风险的，所以最好继承它，然后让需要多表查询的地方直接实例化子类

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重构前

/*功能：查询指定文件夹下的特定页的邮件列表（HTML Table）*/function GetMailList($folderId, $pageNo, $pageSize){    global $db_obj, $pageLink, $html; // db_obj是从外部导入使用，后两个似乎要导出去        $query = " where folderId = $folderId ..."; //省略很多行    $pageclass = new T_Page;    $tableName = "mail";    $condition = $query . "order by tm desc";    $pageclass->BaseSet($tableName, "id,sender,subject,content,...", $pageNo, $pageSize, $db_obj);    $pageclass->SetCondition($condition);        $record = $pageclass->ReadList(); // 查出来的记录集，被放到二维数组里    $pageLink=$pageclass->Page(); //存放翻页按钮的数组    $html = "
     
      ";    for($ipage=0;$ipage<$pageSize;$ipage++)    {        $i=$ipage;        $id = $record[$i]["id"];                $sender = $record[$i]["sender"];        $subject = $record[$i]["subject"];        $content = $record[$i]["content"];                $html = $html . "
";        $html = $html . "
";        ...    }    $html = $html . "
      
       
        
        
$subject
       
      
     
";}/*功能： 查询"一页"记录,且输出导航链接用于翻页*/class T_Page{    var $TableName;    ...        function BaseSet($TableName, $Fields, $PageNo, $PageSize, $Obj_DB)    {        $this->TableName = $TableName;        ...                $this->MaxLine = $this->PageSize;        $this->Offset = $this->PageNo * $this->PageSize;    }        function SetCondition($Condition)    {        $this->Condition = $Condition;    }        function ReadList()    {        $SQL = "select count(*) as recordtotal from $this->tableName $this->Condition";        $result = $this->Obj_DB->simpleQuery($SQL);        $row = $this->Obj_DB->fetchRow($result, DB_FETCHMODE_ASSOC);        $this->Total = $row["recordtotal"];                if($this->Total > 0)        {            $SQL = "select $this->Fields fom $this->tableName $this->Condition limit $this->Offset, $this->MaxLine;";            $result = $this->Obj_DB->simpleQuery($SQL);            $this->Number = $this->Obj_DB->numRows($result);            while($row = $this->Obj_DB->fetchRow($result,DB_FETCHMODE_ASSOC))            {                $this->Result[]=$row;            }            $this->Obj_DB->freeResult($result);        }        return($this->Result)    }        function Page()    {        if($this->PageNo > 0)            $this->PageLink[0] = "上一页";        else            $this->PageLink[0] = "上一页";        ...        return $this->PageLink;    }        // more function}

 

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 重构后

class MailPage extends T_Page{    function setTotal()    {        ...        $this->Total = $row["recordtotal"];    }        function getMailList()    {        $Fields = $this->Field . " ,'' as taglist ";        $SQL.="select $Fields from $this->Table $this->Condition";        $SQL.=" LIMIT $this->Offset , $this->MaxLine";                 ...    }        function addTagList()    {
    　　　　 ...        $tagList = Array();        for($i=0; $i < $this->Number; $i++)        {            $key = $this->Result[$i]["id"];            $this->Result[$i]["taglist"] = $tagList[$key];        }    }        //覆盖父类的接口    function ReadList()    {        $this->setTotal();        $this->getMailList();        $this->addTagList();        return $this->Result;    }    }class TagPage extends MailPage{    function SetCondition($taglist)    {        ...        $this->Condition = sprintf(" where id in (%s) order by tm desc ", $mailList);    }}