如何在Ruby中使用Nokogiri迭代XML嵌套元素

Question

我正试图用Nokogiri迭代XML格式的文件夹结构,但我陷入了困境:

<test>
   <folder name="Folder A">
      <folder name="Folder A1">
         <file name="a.txt">Cool file</file>
      </folder>
      <folder name="Folder A2"></folder>
   </folder>
   <folder name="Folder B">
      <folder name="Folder B1"></folder>
      <folder name="Folder B2">
         <folder name="Folder B21">
            <file name="b.txt"></file>
         </folder>
   </folder>
</test>

因此,我想迭代这个以便能够创建文件夹和文件树(文件夹A1和A2在文件夹A内,文件夹B1和B2在文件夹B内,文件夹B21在文件夹B2内).

所以我这样做:

nodes = allnodes.xpath('//folder')
nodes.each do |node|
  puts "name => #{node.attributes['name']}"
end

但这列出了我所有的文件夹(A,A1,A2,B,B1,B2,B21).我怎么能这样做,以便我不检查以前的文件夹中的更多文件夹,然后我将它发送到相同的递归函数？

非常感谢您的帮助 :)

Answer 1

当您使用XPath时,//foo您可以foo在任何级别找到元素.如果您改为使用./foo或只是foo那时您将只找到子元素.从而:

# Given an XML node, yields the node and all <file> children
# Then recursively does the same with every <folder> child
def process_files_and_folders(node,&blk)   
  yield node, node.xpath('file')
  node.xpath('folder').each{ |folder| process_files_and_folders(folder,&blk) }
end

这个的关键是(a)递归(让所有子文件夹调用本身的方法)和(b)用&blk符号捕获用户传递的块,然后将该块传递给后面的调用.

看到行动:

require 'nokogiri'
doc = Nokogiri.XML(my_xml)
process_files_and_folders( doc.root ) do |folder,files|
  depth  = folder.ancestors.length-1  # Just for pretty text output indenting
  indent = "  "*depth                 # Just for pretty text output indenting
  if folder['name']
    puts "#{indent}Processing the folder named #{folder['name']}"
  else
    puts "#{indent}No folder name; probably the root element."
  end
  unless files.empty?
    puts "#{indent}There are #{files.length} files in '#{folder['name']}':"
    files.each{ |file| print indent, file['name'], "\n" }
  end
end

结果:

No folder name; probably the root element.
  Processing the folder named Folder A
    Processing the folder named Folder A1
    There are 1 files in 'Folder A1':
    a.txt
    Processing the folder named Folder A2
  Processing the folder named Folder B
    Processing the folder named Folder B1
    Processing the folder named Folder B2
      Processing the folder named Folder B21
      There are 1 files in 'Folder B21':
      b.txt