XPath:限制结果集的范围 [英] XPath: limit scope of result set

问题描述

给定 XML

<a>
    <c>
        <b id="1" value="noob"/>
    </c>
    <b id="2" value="tube"/>
    <a>
        <c>
            <b id="3" value="foo"/>
        </c>
        <b id="4" value="goo"/>
        <b id="5" value="noob"/>
        <a>
            <b id="6" value="near"/>
            <b id="7" value="bar"/>
        </a>
    </a>
</a>

和 Xpath 1.0 查询

and the Xpath 1.0 query

//b[@id=2]/ancestor::a[1]//b[@value="noob"]

上面的 Xpath 返回节点 id 1 和 5.目标是将结果限制为节点 id=1，因为它是唯一的 @value="noob" 元素的后代相同 的 (//b[@id=2]) 也是其后代.

The Xpath above returns both node ids 1 and 5. The goal is to limit the result to just node id=1 since it is the only @value="noob" element that is a descendant of the same <a> that (//b[@id=2]) is also a descendant of.

换句话说，查找所有值为noob"的 b 元素，它们是 a 元素的后代，该元素也有一个 id 为 2 的后代，但是不是任何其他 a 元素的后代".怎么这么纠结?实际上，id 编号和值是可变的，并且会有数百种节点类型.

In other words, "Find all b elements who's value is "noob" that are descendants of the a element which also has a descendant whose id is 2, but is not the descendant of any other a element". How's that for convoluted? In practice the id number and values would be variable and there would hundreds of node types.

如果 id=2，我们希望返回元素 id=1 而不是 id=5，因为它包含在另一个 a 元素中.如果 id=4，我们希望返回 id=5，但不会返回 id=1，因为它不在第一个祖先元素中作为 id=4.

If the id=2, we would expect to return element id=1 not id=5 since it is contained in another a element. If the id=4, we would expect to return id=5, but not id=1 since it is not in the first ancestor a element as id=4.

根据 Dimitre 和 Alejandro 的评论，我找到了这个有用的博客说明 count() 与 | 一起使用的条目union 运算符以及其他一些很好的技巧.

Based on the comments of Dimitre and Alejandro, I found this helpful blog entry explaining the use of count() with the | union operator as well as some other excellent tips.

推荐答案

使用:

//b[@value='noob']
      [count(ancestor::a[1] | //b[@id=2]/ancestor::a[1]) = 1]

说明:

第二个谓词确保两个 b 元素具有相同的最近祖先 a.

The second predicate assures that both b elements have the same nearest ancestor a.

记住:在 XPath 1.0 中，节点身份的测试是:

Remember: In XPath 1.0 the test for node identity is:

count($n1 | $n2) = 1

这篇关于XPath:限制结果集的范围的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！