一、 DBQuery对象
现在，我们的DBQuery对象简单地模仿一个存储过程—一旦被执行，即返回一个必须进行保存的结果资源；并且如果你想使用该结果集上的函数（例如num_rows()或fetch_row()）的话，你必须传递MySqlDB对象。那么，如果由DBQuery对象来实现MySqlDB对象（其设计目的是对一个执行查询的结果进行操作）实现的函数，效果如何呢？让我们继续使用上一篇示例中的代码；并且让我们假定，现在由DBQuery对象管理我们的结果资源。DBQuery类的源码如列表1所示。
列表1.使用DBQuery类。
<ol class="dp-c"><li class="alt"><span><span class="keyword">require</span><span> </span><span class="string">'mysql_db.php'</span><span>; </span></span></li><li><span class="keyword">require_once</span><span> </span><span class="string">'query.php'</span><span>; </span></li><li class="alt"><span class="vars">$db</span><span> = </span><span class="keyword">new</span><span> MySqlDb; </span></li><li><span class="vars">$db</span><span>->connect(</span><span class="string">'host'</span><span>， </span><span class="string">'username'</span><span>， </span><span class="string">'pass'</span><span>); </span></li><li class="alt"><span class="vars">$db</span><span>->query(</span><span class="string">'use content_management_system'</span><span>); </span></li><li><span class="vars">$query</span><span> = </span><span class="keyword">new</span><span> DBQuery(</span><span class="vars">$db</span><span>); </span></li><li class="alt"><span class="vars">$query</span><span>->prepare(</span><span class="string">'SELECT fname，sname FROM users WHERE username=:1S AND pword=:2S AND expire_time<:3i><span>); </span><li><span>try { </span></li><li class="alt"><span> </span><span class="keyword">if</span><span>(</span><span class="vars">$query</span><span>->execute(</span><span class="string">"visualad"</span><span>， </span><span class="string">"apron"</span><span>， time()))->num_rows() == 1) { </span></li><li><span></span><span class="func">echo</span><span>(</span><span class="string">'Correct Credentials'</span><span>); </span></li><li class="alt"><span> } </span><span class="keyword">else</span><span> { </span></li><li><span></span><span class="func">echo</span><span>(</span><span class="string">'Incorrect Credentials / Session Expired'</span><span>); </span></li><li class="alt"><span> } </span></li><li><span>} catch (QueryException </span><span class="vars">$e</span><span>) { </span></li><li class="alt"><span> </span><span class="func">echo</span><span>(</span><span class="string">'Error executing query: '</span><span> . </span><span class="vars">$e</span><span>); </span></li><li><span>} </span></li></:3i></span></li></ol>上面修改后的代码中我们最感兴趣的是，catch语句和execute语句。
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◆execute语句不再返回一个结果资源，现在它返回DBQuery对象本身。
◆DBQuery对象现在实现num_rows()函数—我们从DB接口中已经熟悉。
◆如果查询执行失败，它抛出一个QueryException类型的异常。当被转换成一个字符串时，它将返回发生的错误的细节信息。
为此，你需要使用PHP代理。事实上，你在我们的DBQuery对象中已经使用代理了，但是现在将更为深入地使用它来把它与MySqlDB对象紧密绑定。该DBQuery对象已经被使用一个实现DB接口的对象初始化，并且它已经包含一个成员函数execute—由它调用DB对象的query()方法来执行该查询。这个DBQuery对象本身并不实际地查询数据库，它把这项任务交由DB对象来完成。这就是代理，其实是一个进程—借助于这个进程，通过把消息发送给另一个实现相同的或类似行为的对象，一个对象可以实现一个特别的行为。
为此，你需要修改DBQuery对象以便包括所有的函数—它们操作一个来自DB对象的结果资源。当执行查询以调用DB对象的相应函数并且返回它的结果时，你需要使用存储的结果。下列函数将被添加：
列表2:使用代理扩展DBQuery类。
<ol class="dp-c"><li class="alt"><span><span class="keyword">class</span><span> DBQuery </span></span></li><li><span>{ </span></li><li class="alt"><span> ..... </span></li><li><span> </span></li><li class="alt"><span> </span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> fetch_array() </span></li><li><span> { </span></li><li class="alt"><span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) { </span></li><li><span> </span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>); </span></li><li class="alt"><span>} </span></li><li><span> </span></li><li class="alt"><span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->fetch_array(</span><span class="vars">$this</span><span>->result); </span></li><li><span> } </span></li><li class="alt"><span> </span></li><li><span> </span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> fetch_row() </span></li><li class="alt"><span> { </span></li><li><span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) { </span></li><li class="alt"><span> </span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>); </span></li><li><span>} </span></li><li class="alt"><span> </span></li><li><span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->fetch_row(</span><span class="vars">$this</span><span>->result); </span></li><li class="alt"><span> } </span></li><li><span> </span></li><li class="alt"><span> </span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> fetch_assoc() </span></li><li><span> { </span></li><li class="alt"><span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) { </span></li><li><span> </span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>); </span></li><li class="alt"><span>} </span></li><li><span> </span></li><li class="alt"><span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->fetch_assoc(</span><span class="vars">$this</span><span>->result); </span></li><li><span> } </span></li><li class="alt"><span> </span></li><li><span> </span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> fetch_object() </span></li><li class="alt"><span> { </span></li><li><span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) { </span></li><li class="alt"><span> </span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>); </span></li><li><span>} </span></li><li class="alt"><span> </span></li><li><span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->fetch_object(</span><span class="vars">$this</span><span>->result); </span></li><li class="alt"><span> } </span></li><li><span> </span></li><li class="alt"><span> </span><span class="keyword">public</span><span> </span><span class="keyword">function</span><span> num_rows() </span></li><li><span> { </span></li><li class="alt"><span></span><span class="keyword">if</span><span> (! </span><span class="func">is_resource</span><span>(</span><span class="vars">$this</span><span>->result)) { </span></li><li><span> </span><span class="keyword">throw</span><span> </span><span class="keyword">new</span><span> Exception(</span><span class="string">'Query not executed.'</span><span>); </span></li><li class="alt"><span>} </span></li><li><span> </span></li><li class="alt"><span></span><span class="keyword">return</span><span> </span><span class="vars">$this</span><span>->db->num_rows(</span><span class="vars">$this</span><span>->result); </span></li><li><span> } </span></li><li class="alt"><span>} </span></li></ol>每个函数的实现相当简单。它首先进行检查，以确保已经执行查询，然后把任务代理到DB对象，返回它的结果就好象它是查询对象本身（称作是基本数据库函数）一样。 1
