perl - 如何遍历到前一个父节点并获取XPath中元素的值？

标签 perl xpath-2.0

我试图获取 XPath 中前一个节点的值，但我要么得到重复值，要么没有值。

代码如下:

use XML::LibXML;

my %chapter_columns = (
  'Chapter_Id'         => '@id',
  'Chapter_Title'      => 'book:locator[contains(@xlink:href, "format=epub")]/@xlink:title',
  'Chapter_Doi_Prefix' => 'substring-before(book:meta/@doi,"/")',
  'Book_Publisher'     => '//@publisherId',
  'Book_Platform'      => '//@platform',
);

my $parser = XML::LibXML->new();
my $dom    = $parser->parse_file("test.xml");
my $root   = $dom->documentElement();
my $xpc    = XML::LibXML::XPathContext->new($root);

$xpc->registerNs('book',  'http://api.abc.org/Book/1.0/');
$xpc->registerNs('xlink', 'http://www.w3.org/1999/xlink');

foreach my $chapter_node ($xpc->findnodes('/book:bookResource/book:book/book:contents/book:chapter')) {
  foreach my $col (qw/Chapter_Id Book_Publisher Book_Platform/) {
    print $xpc->findvalue($chapter_columns{$col}, $chapter_node) . "\n";
  }
}

我尝试使用//@publisherId 和//@platform 获取“publisherId”和“platform”的值。它们为每本书产生重复的值(value)。我什至尝试获取它们“../../@publisherId”；但没有获得任何值(value)。

我不想更改 foreach 循环中定义的 xpath，但打算向后遍历。 我怎样才能实现这一目标？

我得到的结果是:

Chapter_Id=bk444444ch1
Book_Publisher=BKCBKC
Book_Platform=ScienceScience
Chapter_Id=bk444444ch2
Book_Publisher=BKCBKC
Book_Platform=ScienceScience
Chapter_Id=bk444444ch1
Book_Publisher=BKCBKC
Book_Platform=ScienceScience
Chapter_Id=bk444444ch2
Book_Publisher=BKCBKC
Book_Platform=ScienceScience

而我想要:

Chapter_Id=bk444444ch1
Book_Publisher=BKC
Book_Platform=Science
Chapter_Id=bk444444ch2
Book_Publisher=BKC
Book_Platform=Science
Chapter_Id=bk444444ch1
Book_Publisher=BKC
Book_Platform=Science
Chapter_Id=bk444444ch2
Book_Publisher=BKC
Book_Platform=Science

XML如下:

<?xml version="1.0" encoding="UTF-8"?>
<book:bookResource xmlns:book="http://api.abc.org/Book/1.0/">
  <book:book>
    <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
      4444-1000-17?releaseStatus=RELEASED" xlink:title="979-0-4444-1000-17"
      xlink:type="locator">
    </book:locator>
    <book:meta coverImage="/blank-cover.gif" publisherId="BKC" platform="Science"
      doi="10.1088/bk444444" publicationDate="2016-12-01" issn="1111-222X"
      collectionId="0001" lastModified="2013-07-05T09:03:40+05:30" releaseStatus="RELEASED">
    </book:meta>
    <book:contents>
      <book:chapter id="bk444444ch1" type="CHAPTER">
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED"
          xlink:role="http://www.abc.org/roles/book-part-locator" xlink:title="Photonic" xlink:type="locator">
        </book:locator>  
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;format=pdf"
          xlink:role="http://www.abc.org/roles/book-part-pdf-locator" xlink:title="Photonic
          crystal light-emitting sources" xlink:type="locator">
        </book:locator>  
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;format=epub"
          xlink:role="http://www.abc.org/roles/book-part-epub-locator" xlink:title="Photonic
          crystal light-emitting sources" xlink:type="locator">
        </book:locator>  
        <book:meta doi="10.1088/bk444444ch1" firstPage="1-1" lastPage="1-118"> 
          <book:author givenName="J E" surname="Field"> 
            <book:affiliation xmlns:xlink="http://www.w3.org/1999/xlink"
              xlink:href="bk444444ch1af1" xlink:role="http://www.abc.org/roles/affiliation-locator"
              xlink:type="locator">
            </book:affiliation>
          </book:author>  
          </book:meta>
      </book:chapter>
      <book:chapter id="bk444444ch2" type="CHAPTER"> 
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch2?releaseStatus=RELEASED"
          xlink:role="http://www.abc.org/roles/book-part-locator" xlink:title="The effect of
          long-range order on the elastic properties of Cu3Au" xlink:type="locator">
        </book:locator>
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch2?releaseStatus=RELEASED&amp;format=pdf"
          xlink:role="http://www.abc.org/roles/book-part-pdf-locator" xlink:title="The effect of
          long-range order" xlink:type="locator">
        </book:locator>
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch2?releaseStatus=RELEASED&amp;format=epub"
          xlink:role="http://www.abc.org/roles/book-part-epub-locator" xlink:title="The effect of
          long-range order" xlink:type="locator">
        </book:locator>
        <book:meta doi="10.1088/bk444444ch2" firstPage="2-1" lastPage="2-35">
          <book:affiliation name="Department of Physics">
            <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bk444444ch2af1"
              xlink:role="http://www.abc.org/roles/affiliation-locator" xlink:type="locator">
            </book:locator>
          </book:affiliation>
        </book:meta>
      </book:chapter>
    </book:contents>
  </book:book>
  <book:book>
    <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
      4444-1000-17?releaseStatus=RELEASED" xlink:title="979-0-4444-1000-17"
      xlink:type="locator">
    </book:locator> 
    <book:meta coverImage="/blank-cover.gif" publisherId="BKC" platform="Science"
      doi="10.1088/bk444444" publicationDate="2016-12-01" issn="1111-222X"
      collectionId="0001" lastModified="2013-07-05T09:03:40+05:30" releaseStatus="RELEASED">
    </book:meta>
    <book:contents>
      <book:chapter id="bk444444ch1" type="CHAPTER">
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED"
          xlink:title="Photonic crystal" xlink:type="locator">
        </book:locator>  
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;format=pdf"
          xlink:title="Photonic
          crystal light-emitting sources" xlink:type="locator">
        </book:locator>  
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;format=epub" xlink:title="Photonic
          crystal" xlink:type="locator">
        </book:locator>  
        <book:meta doi="10.1088/bk444444ch1" firstPage="1-1" lastPage="1-118"> 
        </book:meta>
      </book:chapter>
      <book:chapter id="bk444444ch2" type="CHAPTER"> 
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch2?releaseStatus=RELEASED"
          xlink:role="http://www.abc.org/roles/book-part-locator" xlink:title="The effect of
          long-range order on the elastic properties of Cu3Au" xlink:type="locator">
        </book:locator>
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch2?releaseStatus=RELEASED&amp;format=pdf"
          xlink:role="http://www.abc.org/roles/book-part-pdf-locator" xlink:title="The effect of
          long-range order on the elastic properties of Cu3Au" xlink:type="locator">
        </book:locator>
        <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/book/isbn/979-0-
          4444-1000-17/book-part/chapter/bk444444ch2?releaseStatus=RELEASED&amp;format=epub"
          xlink:role="http://www.abc.org/roles/book-part-epub-locator" xlink:title="The effect of
          long-range order on the elastic properties of Cu3Au" xlink:type="locator">
        </book:locator>
        <book:meta doi="10.1088/bk444444ch2" firstPage="2-1" lastPage="2-35">
          <book:affiliation name="Department of Physics, University of San Salvador">
            <book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bk444444ch2af1"
              xlink:type="locator">
            </book:locator>
          </book:affiliation>
        </book:meta>
      </book:chapter>
    </book:contents>
  </book:book>
</book:bookResource>

最佳答案

像 //@publisherId 这样的 XPath 表达式会查找文档root 下的所有 publisherId 属性。 (.//@publisherId 查找当前节点下的所有此类属性，但这也不是您想要的。)

您需要使用 ancestor 轴查找包含此 chapter 的 book 元素，然后从 访问属性meta 元素是该书的子元素。这段代码运行良好。

use strict;
use warnings;

use XML::LibXML;

my %chapter_columns = (
  Chapter_Id         => '@id',
  Chapter_Title      => 'book:locator[contains(@xlink:href, "format=epub")]/@xlink:title',
  Chapter_Doi_Prefix => 'substring-before(book:meta/@doi,"/")',
  Book_Publisher     => 'ancestor::book:book/book:meta/@publisherId',
  Book_Platform      => 'ancestor::book:book/book:meta/@platform',                       
);

my $parser = XML::LibXML->new;
my $dom    = $parser->parse_file('test.xml');
my $xpc    = XML::LibXML::XPathContext->new($dom);

$xpc->registerNs('book', 'http://api.abc.org/Book/1.0/');
$xpc->registerNs('xlink', 'http://www.w3.org/1999/xlink');

my @chapters = $xpc->findnodes('/book:bookResource/book:book/book:contents/book:chapter');

foreach my $chapter (@chapters) {
  foreach my $col(qw/Chapter_Id Book_Publisher Book_Platform/) {
    printf "%s=%s\n", $col, $xpc->findvalue($chapter_columns{$col}, $chapter);
  }
  print "\n";
}

但是，我首先查找所有 book 元素，保存 meta/@publisherId 和 meta/@platform 属性，然后列出所有同一本书的 contents/chapter 元素。像这样

my @books = $xpc->findnodes('/book:bookResource/book:book');

for my $book (@books) {

  my $publisher = $xpc->findvalue('book:meta/@publisherId', $book);
  my $platform = $xpc->findvalue('book:meta/@platform', $book);

  my @chapters = $xpc->findnodes('book:contents/book:chapter', $book);
  for my $chapter (@chapters) {

    my $chapter_id = $xpc->findvalue('@id', $chapter);

    print "Chapter_Id=$chapter_id\n";
    print "Book_Publisher=$publisher\n";
    print "Book_Platform=$platform\n";
    print "\n";
  }
}

两种样式产生相同的输出:

Chapter_Id=bk444444ch1
Book_Publisher=BKC
Book_Platform=Science

Chapter_Id=bk444444ch2
Book_Publisher=BKC
Book_Platform=Science

Chapter_Id=bk444444ch1
Book_Publisher=BKC
Book_Platform=Science

Chapter_Id=bk444444ch2
Book_Publisher=BKC
Book_Platform=Science

关于perl - 如何遍历到前一个父节点并获取XPath中元素的值？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/17771752/

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