是否有“if -then - else"?XPath 中的语句? [英] Is there an "if -then - else " statement in XPath?

问题描述

似乎有了 xpath 中所有丰富的功能，您就可以执行 "if" .然而，我的引擎一直坚持没有这样的功能"，我在网上几乎找不到任何文档(我发现了一些可疑的来源，但它们的语法不起作用)

我需要从字符串的末尾删除 ':'(如果存在)，所以我想这样做:

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

有什么建议吗?

解决方案

是的，在 XPath 1.0 中有一种方法可以做到:

<前>连接(substring($s1, 1, number($condition) * string-length($s1)),substring($s2, 1, number(not($condition)) * string-length($s2)))

这依赖于两个互斥字符串的连接，如果条件为假，第一个为空 (0 * string-length(...))，第二个为空，如果条件为真.这称为贝克尔方法"，归因于 Oliver Becker (原始链接现已失效，网络存档有一个副本).

就你而言:

<前>连接(子串(substring-before(//div[@id='head']/text(), ': '),1、数字(结尾(//div[@id='head']/text()，':'))* string-length(substring-before(//div [@id='head']/text(), ':'))),子串(//div[@id='head']/text(),1、数字(不是(结尾(//div[@id='head']/text()，':')))* 字符串长度(//div[@id='head']/text())))

虽然我会尝试去掉之前所有的 "//".

此外，//div[@id='head'] 有可能返回多个节点.
请注意这一点 - 使用 //div[@id='head'][1] 更具防御性.

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)

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())

Any advice?

解决方案

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))
)

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 (original link is now dead, the web archive has a copy).

In your case:

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())
  )
)

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

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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