如何用带嵌套条件（引用外部元素值）的XPath查询符合条件的书籍

需要查询XML中作者获奖的书籍，同时输出书籍名称和对应作者的宠物名。XML结构中仅含一个城市，但包含大量书籍与作者，尝试的XPath语句无法正确关联当前书籍对应的作者。

XML示例 #

<?xml version="1.0" encoding="UTF-8"?>
<root>
  <books>
    <book>
      <name>Fantastic World of Peggy</name>
      <category>fiction</category>
      <author-ref>/SanDiego/Peter</author-ref>
    </book>
  </books>
  <cities>
    <name>SanDiego</name>
    <authors>
      <author>
        <name>Peter</name>
        <awards-won>true</awards-won>
        <pet>pike</pet>
      </author>
    </authors>
  </cities>
</root>

尝试的无效XPath语句 #

//books[category = 'fiction' and //author[name = string-after(<the-current-book>/author-ref, '/SanDiego/') and awards-won = 'true']]

//books[category = 'fiction']/concat(name, concat(' - ', //author[name = string-after(<the-current-book>/author-ref, '/SanDiego/') and awards-won = 'true']/pet))

可行的XPath写法 #

1. XPath 1.0 版本 #

XPath 1.0不支持string-after，需用substring-after处理作者引用，核心是用**当前上下文节点.**指代当前book，避免全局查询的匹配错误：

筛选符合条件的书籍节点

//book[category='fiction' and /root/cities/authors/author[name=substring-after(./author-ref, '/SanDiego/') and awards-won='true']]

直接输出书籍名称与作者宠物名的组合

//book[category='fiction' and /root/cities/authors/author[name=substring-after(./author-ref, '/SanDiego/') and awards-won='true']]/concat(name, ' - ', /root/cities/authors/author[name=substring-after(current()/author-ref, '/SanDiego/') and awards-won='true']/pet)

2. XPath 2.0+ 版本 #

支持string-after，写法更简洁，可用current()明确指代当前上下文的book节点：

筛选书籍节点

//book[category='fiction' and /root/cities/authors/author[name=string-after(author-ref, '/SanDiego/') and awards-won='true']]

输出组合内容

//book[category='fiction' and /root/cities/authors/author[name=string-after(author-ref, '/SanDiego/') and awards-won='true']]/concat(name, ' - ', /root/cities/authors/author[name=string-after(current()/author-ref, '/SanDiego/') and awards-won='true']/pet)

关键说明 #

• 用.或current()替代你之前的<the-current-book>占位符，精准指代当前遍历的book节点；
• 限定作者查询路径为/root/cities/authors/author，避免全局//author带来的无关匹配；
• XPath 1.0需用substring-after替代string-after，后者是2.0及以上版本的专属函数。

内容的提问来源于stack exchange，提问作者RedX