是否有“if -then - else”在XPath中的声明？ [英] Is there an "if -then - else " statement in XPath?

问题描述

似乎xpath中的所有丰富功能都可以执行if。但是，我的引擎一直坚持没有这样的功能，我几乎没有在网上找到任何文档（我发现了一些可疑的来源，但他们的语法不起作用）

It seems with all the rich amount of function in xpath that you could do an "if" . However , my engine keeps insisting "there is no such function" , and I hardly find any documentation on the web (I found some dubious sources , but the syntax they had didn't work)

我需要从字符串末尾删除'：'（如果存在），所以我想这样做：

I need to remove ':' from the end of a string (if exist), so I wanted to do this:

if (fn:ends-with(//div [@id='head']/text(),': '))
            then (fn:substring-before(//div [@id='head']/text(),': ') )
            else (//div [@id='head']/text())

有什么建议吗？

推荐答案

是的，有一种方法可以在XPath 1.0中实现：

Yes, there is a way to do it in XPath 1.0:

concat(
  substring($s1, 1, number($condition)      * string-length($s1)),
  substring($s2, 1, number(not($condition)) * string-length($s2))
)

这取决于两个串联互斥字符串，如果条件为假，则第一个为空（ 0 * string-length（...）），如果条件为真，则第二个为空。这被称为Becker的方法，归功于 Oliver Becker 。

This relies on the concatenation of two mutually exclusive strings, the first one being empty if the condition is false (0 * string-length(...)), the second one being empty if the condition is true. This is called "Becker's method", attributed to Oliver Becker.

在您的情况下：

concat(
  substring(
    substring-before(//div[@id='head']/text(), ': '),
    1, 
    number(
      ends-with(//div[@id='head']/text(), ': ')
    )
    * string-length(substring-before(//div [@id='head']/text(), ': '))
  ),
  substring(
    //div[@id='head']/text(), 
    1, 
    number(not(
      ends-with(//div[@id='head']/text(), ': ')
    ))
    * string-length(//div[@id='head']/text())
  )
)

虽然我会尝试在之前摆脱所有//。

Though I would try to get rid of all the "//" before.

此外，有可能 // div [@ id ='head'] 返回多个节点。

请注意这一点—使用 // div [@ id ='head'] [1] 更具防御性。

Also, there is the possibility that //div[@id='head'] returns more than one node.
Just be aware of that — using //div[@id='head'][1] is more defensive.

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