怎樣結合registerXPathNamespace 和自定義XPath 函數來擴展XML 查詢功能？

M66 2025-07-08

在使用PHP 處理XML 數據時， DOMDocument和DOMXPath是兩個非常強大的工具。尤其是在需要進行複雜XML 查詢的時候，利用命名空間與XPath 表達式可以大大提升靈活性與準確性。本文將介紹如何結合registerXPathNamespace方法和自定義XPath 函數，來擴展和增強你的XML 查詢功能。

一、理解命名空間在XPath 中的重要性

在許多XML 文檔中，元素和屬性通常帶有命名空間前綴。例如：

 <span><span><span class="hljs-tag">&lt;<span class="hljs-name">root</span></span></span><span> </span><span><span class="hljs-attr">xmlns:h</span></span><span>=</span><span><span class="hljs-string">"http://www.w3.org/TR/html4/"</span></span><span>&gt;
  </span><span><span class="hljs-tag">&lt;<span class="hljs-name">h:table</span></span></span><span>&gt;
    </span><span><span class="hljs-tag">&lt;<span class="hljs-name">h:tr</span></span></span><span>&gt;
      </span><span><span class="hljs-tag">&lt;<span class="hljs-name">h:td</span></span></span><span>&gt;Apples</span><span><span class="hljs-tag">&lt;/<span class="hljs-name">h:td</span></span></span><span>&gt;
      </span><span><span class="hljs-tag">&lt;<span class="hljs-name">h:td</span></span></span><span>&gt;Bananas</span><span><span class="hljs-tag">&lt;/<span class="hljs-name">h:td</span></span></span><span>&gt;
    </span><span><span class="hljs-tag">&lt;/<span class="hljs-name">h:tr</span></span></span><span>&gt;
  </span><span><span class="hljs-tag">&lt;/<span class="hljs-name">h:table</span></span></span><span>&gt;
</span><span><span class="hljs-tag">&lt;/<span class="hljs-name">root</span></span></span><span>&gt;
</span></span>

要正確查詢如<h:td>這樣的節點，XPath 表達式需要知道前綴h對應的命名空間URI。這就是registerXPathNamespace派上用場的時候。

 <span><span><span class="hljs-variable">$xml</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title class_">DOMDocument</span></span><span>();
</span><span><span class="hljs-variable">$xml</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">loadXML</span></span><span>(</span><span><span class="hljs-variable">$yourXmlString</span></span><span>);
</span><span><span class="hljs-variable">$xpath</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title class_">DOMXPath</span></span><span>(</span><span><span class="hljs-variable">$xml</span></span><span>);
</span><span><span class="hljs-variable">$xpath</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">registerNamespace</span></span><span>(</span><span><span class="hljs-string">"h"</span></span><span>, </span><span><span class="hljs-string">"http://www.w3.org/TR/html4/"</span></span><span>);
</span><span><span class="hljs-variable">$tds</span></span><span> = </span><span><span class="hljs-variable">$xpath</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">query</span></span><span>(</span><span><span class="hljs-string">"//h:td"</span></span><span>);
</span></span>

二、自定義XPath 函數的動機

雖然XPath 語言本身功能強大，但在某些業務邏輯場景下，內建的XPath 函數可能無法滿足需求。例如，我們可能想通過一個函數來判斷某個元素的值是否在數據庫或數組中出現，或者進行更複雜的字符串處理。

PHP 原生並不支持向XPath 注入自定義函數，但可以通過變通方式，例如在遍歷查詢結果時調用PHP 函數實現邏輯，或者結合libxml和XSLTProcessor來部分模擬該功能。

但更常見的做法是，在使用XPath 查詢前，先註冊命名空間並預處理XML，再配合自定義函數操作節點集。

三、結合命名空間和自定義邏輯的實際案例

假設你有如下XML 文檔，包含多個帶命名空間的<item>節點：

 <span><span><span class="hljs-tag">&lt;<span class="hljs-name">catalog</span></span></span><span> </span><span><span class="hljs-attr">xmlns:bk</span></span><span>=</span><span><span class="hljs-string">"http://example.com/book"</span></span><span>&gt;
  </span><span><span class="hljs-tag">&lt;<span class="hljs-name">bk:item</span></span></span><span>&gt;
    </span><span><span class="hljs-tag">&lt;<span class="hljs-name">bk:title</span></span></span><span>&gt;PHP 程式設計</span><span><span class="hljs-tag">&lt;/<span class="hljs-name">bk:title</span></span></span><span>&gt;
    </span><span><span class="hljs-tag">&lt;<span class="hljs-name">bk:price</span></span></span><span>&gt;45</span><span><span class="hljs-tag">&lt;/<span class="hljs-name">bk:price</span></span></span><span>&gt;
  </span><span><span class="hljs-tag">&lt;/<span class="hljs-name">bk:item</span></span></span><span>&gt;
  </span><span><span class="hljs-tag">&lt;<span class="hljs-name">bk:item</span></span></span><span>&gt;
    </span><span><span class="hljs-tag">&lt;<span class="hljs-name">bk:title</span></span></span><span>&gt;Java 程式設計</span><span><span class="hljs-tag">&lt;/<span class="hljs-name">bk:title</span></span></span><span>&gt;
    </span><span><span class="hljs-tag">&lt;<span class="hljs-name">bk:price</span></span></span><span>&gt;55</span><span><span class="hljs-tag">&lt;/<span class="hljs-name">bk:price</span></span></span><span>&gt;
  </span><span><span class="hljs-tag">&lt;/<span class="hljs-name">bk:item</span></span></span><span>&gt;
</span><span><span class="hljs-tag">&lt;/<span class="hljs-name">catalog</span></span></span><span>&gt;
</span></span>

你希望查詢所有價格低於50 元的圖書標題。 XPath 本身支持數字比較：

 <span><span><span class="hljs-variable">$xpath</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">registerNamespace</span></span><span>(</span><span><span class="hljs-string">"bk"</span></span><span>, </span><span><span class="hljs-string">"http://example.com/book"</span></span><span>);
</span><span><span class="hljs-variable">$nodes</span></span><span> = </span><span><span class="hljs-variable">$xpath</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">query</span></span><span>(</span><span><span class="hljs-string">"//bk:item[bk:price &lt; 50]/bk:title"</span></span><span>);

</span><span><span class="hljs-keyword">foreach</span></span><span> (</span><span><span class="hljs-variable">$nodes</span></span><span> </span><span><span class="hljs-keyword">as</span></span><span> </span><span><span class="hljs-variable">$node</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$node</span></span><span>-&gt;nodeValue . </span><span><span class="hljs-string">"\n"</span></span><span>;
}
</span></span>

如果你要實現更複雜的邏輯（如價格低於50 且標題包含“PHP”），可以結合多個XPath 條件：

 <span><span><span class="hljs-variable">$nodes</span></span><span> = </span><span><span class="hljs-variable">$xpath</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">query</span></span><span>(</span><span><span class="hljs-string">"//bk:item[bk:price &lt; 50 and contains(bk:title, 'PHP')]/bk:title"</span></span><span>);
</span></span>

但若邏輯更加複雜，如“只保留標題包含關鍵詞表中任意一個詞的節點”，則需在查詢後配合自定義函數過濾結果：

 <span><span><span class="hljs-variable">$keywords</span></span><span> = [</span><span><span class="hljs-string">'PHP'</span></span><span>, </span><span><span class="hljs-string">'MySQL'</span></span><span>, </span><span><span class="hljs-string">'Laravel'</span></span><span>];
</span><span><span class="hljs-variable">$nodes</span></span><span> = </span><span><span class="hljs-variable">$xpath</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">query</span></span><span>(</span><span><span class="hljs-string">"//bk:item/bk:title"</span></span><span>);

</span><span><span class="hljs-keyword">foreach</span></span><span> (</span><span><span class="hljs-variable">$nodes</span></span><span> </span><span><span class="hljs-keyword">as</span></span><span> </span><span><span class="hljs-variable">$node</span></span><span>) {
    </span><span><span class="hljs-keyword">foreach</span></span><span> (</span><span><span class="hljs-variable">$keywords</span></span><span> </span><span><span class="hljs-keyword">as</span></span><span> </span><span><span class="hljs-variable">$word</span></span><span>) {
        </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">stripos</span></span><span>(</span><span><span class="hljs-variable">$node</span></span><span>-&gt;nodeValue, </span><span><span class="hljs-variable">$word</span></span><span>) !== </span><span><span class="hljs-literal">false</span></span><span>) {
            </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$node</span></span><span>-&gt;nodeValue . </span><span><span class="hljs-string">"\n"</span></span><span>;
            </span><span><span class="hljs-keyword">break</span></span><span>;
        }
    }
}
</span></span>

雖然這是在XPath 查詢結果外部進行的邏輯處理，但本質上就是將XPath 查詢能力和PHP 自定義邏輯結合。

四、拓展閱讀：結合XSLT 使用自定義函數（進階）

如果你需要真正將PHP 函數嵌入XPath 邏輯中，可以考慮通過XSLTProcessor和PHP 擴展函數結合。例如，通過註冊擴展函數實現邏輯判斷（如php:functionString('your_function') ）——這屬於更高階的用法，需要在PHP 中啟用xsl擴展，並註意安全性。

registerXPathNamespace