xpath：contains（）用于一组答案 [英] xpath: contains() for a group of answers

问题描述

我正在尝试学习XPath，但是在进行嵌套搜索（使用包含）时遇到了麻烦。

I'm trying to learn XPath, and I am having trouble with doing a nested search (using contains).

具体来说，我遇到了以下问题：

Specifically, I was given the following question:

根据以下dtd，有作者列表和书籍列表：

There is a list of authors, and a list of books, according to the following dtd:

<!ELEMENT db1 (book*, author*)>
<!ELEMENT book (title)>
<!ATTLIST book
    bid ID #REQUIRED
    authors IDREFS #REQUIRED
>
<!ELEMENT title (#PCDATA)>
<!ELEMENT author (#PCDATA)>
<!ATTLIST author
    aid ID #REQUIRED
>

编写一个XPath表达式，该表达式返回写书的作者人数。可以假设没有两个包含彼此的作者ID。

Write an XPath expression that returns the number of authors who wrote books. It is possible to assume that there are no two author ids that contain one another.

我尝试了很多事情，但始终收到错误消息：包含的项目过多。
我正在尝试运行以下命令：

I tried many things, but I keep getting an error of "Too many items in contains". I am trying to run something like this:

//author/@aid[contains(//book/@authors/string(.),  string(.))]

我正在使用以下xml文件例如：

I am using the following xml file as an example:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE db1 SYSTEM "C:\blabla\db1.dtd">
<db1>
<book authors="a1 a3 a4" bid="b1">
<title>Book 1</title>
</book>
<book authors="a1 a2 a3" bid="b2">
<title>Book 2</title>
</book>
<book authors="a4" bid="b3">
<title>Book 3</title>
</book>
<author aid="a1"></author>
<author aid="a91"></author>
<author aid="a2"></author>
<author aid="a88"></author>
<author aid="a3"></author>
<author aid="a4"></author>
<author aid="a5"></author>
<author aid="a6"></author>

</db1>

预期答案应该是

a1 a2 a3 a4

有什么建议吗？

谢谢。

推荐答案

我找到了想要的答案。其实并不难，只需熟悉XPath的 id功能即可。

I found the answer I was looking for. It is not that difficult actually, it is just necessary to be familiar with the 'id' feature of XPath.

对此的XPAth查询是：
count（id（// book / @ authors））

The XPAth query for this is: count(id(//book/@authors))

作者列表可以为 id（// book / @ authors）。请注意，此xquery返回完整的xml（而非仅名称）：

The list of authors could be given as id(//book/@authors). Notice that this xquery returns the full xml (and not the names only):

<author aid="a1"/>
<author aid="a2"/>
<author aid="a3"/>
<author aid="a4"/>

请参见引用。

函数包含在

id函数通过元素的唯一ID选择元素。当id的参数为node-set类型时，则结果是将id应用于参数node-set中每个节点的字符串值的结果的并集。当id的参数为任何其他类型时，该参数将转换为字符串，就像通过调用string函数一样；字符串被分成一个由空格分隔的令牌列表（空格是与产品S匹配的任何字符序列）；结果是一个节点集，其中包含与上下文节点相同的文档中的元素，这些元素的唯一ID等于列表中的任何标记。

The id function selects elements by their unique ID. When the argument to id is of type node-set, then the result is the union of the result of applying id to the string-value of each of the nodes in the argument node-set. When the argument to id is of any other type, the argument is converted to a string as if by a call to the string function; the string is split into a whitespace-separated list of tokens (whitespace is any sequence of characters matching the production S); the result is a node-set containing the elements in the same document as the context node that have a unique ID equal to any of the tokens in the list.

这篇关于xpath：contains（）用于一组答案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！