XPath - (//first///*)[1] vs//first////[1] [英] XPath - (//first//*)[1] vs //first//*[1]

问题描述

XPath -(//first//*)[1] 和 //first//*[1] 有什么区别?它是如何工作的?

XPath - What is the difference between (//first//*)[1] and //first//*[1] ? How it works?

示例 XML 文件是:

A sample XML file is:

<root> 
    <first>
             <second>
              Test
             </second>

             <second>
              <third>Test2</third>
         </second>

    </first>
</root>

(//first///*)[1] 给出:

<second>
 Test
</second>

但是//first///*[1] 给出:

  <second>
    Test
  </second>
<third>Test2</third>  

推荐答案

两种情况下，//first选择所有first元素，//first//* 选择 first 的所有元素后代.那么，区别在于:

In both cases, //first select all first elements, and //first//* selects all elements descendents of first. Then, the difference is:

1. (//first//*)[1] 从所有这些元素中选择，只有 first.
2. //first///*[1] 从所有这些元素中选择每个第一个子元素.

1. (//first//*)[1] selects from all of those elements, only the first.
2. //first//*[1] selects from all of those elements, every first child.

正如您在 XML 中看到的那样，second 被 XPath #1 选中，因为它是第一个第一.(您的元素名称选择有点不理想.)second 和 third 都被 XPath #2 选中，因为它们都是 <强>在他们各自的兄弟姐妹中排名第一.

As you've seen for your XML, second is selected by XPath #1 because it is the first of all the descendents of first. (Your element name choices are a bit non-ideal.) Both second and third are selected by XPath #2 because they're both first among their respective siblings.

这篇关于XPath - (//first///*)[1] vs//first////[1]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！