How to avoid creating non-significant white space

2019-06-16 04:20发布

站内问答 / 后端开发
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While parsing an indented XML, non-significant white space text nodes are created from the white spaces between a closing and an opening tag. For example, from the following XML:

<note>
  <to>Tove</to>
  <from>Jani</from>
  <heading>Reminder</heading>
  <body>Don't forget me this weekend!</body>
</note>

whose string representation is as follows,

 "<note>\n  <to>Tove</to>\n  <from>Jani</from>\n  <heading>Reminder</heading>\n  <body>Don't forget me this weekend!</body>\n</note>\n"

the following Document is created:

#(Document:0x3fc07e4540d8 {
  name = "document",
  children = [
    #(Element:0x3fc07ec8629c {
      name = "note",
      children = [
        #(Text "\n  "),
        #(Element:0x3fc07ec8089c {
          name = "to",
          children = [ #(Text "Tove")]
          }),
        #(Text "\n  "),
        #(Element:0x3fc07e8d8064 {
          name = "from",
          children = [ #(Text "Jani")]
          }),
        #(Text "\n  "),
        #(Element:0x3fc07e8d588c {
          name = "heading",
          children = [ #(Text "Reminder")]
          }),
        #(Text "\n  "),
        #(Element:0x3fc07e8cf590 {
          name = "body",
          children = [ #(Text "Don't forget me this weekend!")]
          }),
        #(Text "\n")]
      })]
  })

Here, there are lots of white space nodes of type Nokogiri::XML::Text.

I would like to count the children of each node in a Nokogiri XML Document, and access the first or last child, excluding non-significant white spaces. I wish not to parse them, or distinguish between those and significant text nodes such as those inside the element <to>, like "Tove". Here is an rspec of what I am looking for:

require 'nokogiri'
require_relative 'spec_helper'

xml_text = <<XML
<note>
  <to>Tove</to>
  <from>Jani</from>
  <heading>Reminder</heading>
  <body>Don't forget me this weekend!</body>
</note>
XML

xml = Nokogiri::XML(xml_text)

def significant_nodes(node)
  return 0
end

describe "Stackoverflow Question" do
  it "should return the number of significant nodes in nokogiri." do
    expect(significant_nodes(xml.css('note'))).to eq 4
  end
end

I want to know how to create the significant_nodes function.

If I change the XML to:

<note>
  <to>Tove</to>
  <from>Jani</from>
  <heading>Reminder</heading>
  <body>Don't forget me this weekend!</body>
  <footer></footer>
</note>

then when I create the Document, I still would like the footer represented; using config.noblanks is not an option.

3条回答
虎瘦雄心在
2楼-- · 2019-06-16 04:58

You can create a query that only returns element nodes, and ignores text nodes. In XPath, * only returns elements, so the query could look like (querying the whole doc):

doc.xpath('//note/*')

or if you want to use CSS:

doc.css('note > *')

If you want to implement your significant_nodes method, you would need to make the query relative to the node passed in:

def significant_nodes(node)
  node.xpath('./*').size
end

I don’t know how to do a relative query with CSS, you might need to stick with XPath.

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萌系小妹纸
3楼-- · 2019-06-16 05:04

You can use the NOBLANKS option for parsing the XML string, consider this example:

require 'nokogiri'

string = "<foo>\n  <bar>bar</bar>\n</foo>"
puts string
# <foo>
#   <bar>bar</bar>
# </foo>

document_with_blanks = Nokogiri::XML.parse(s)

document_without_blanks = Nokogiri::XML.parse(s) do |config|
  config.noblanks
end

document_with_blanks.root.children.each { |child| p child }
#<Nokogiri::XML::Text:0x3ffa4e153dac "\n  ">
#<Nokogiri::XML::Element:0x3fdce3f78488 name="bar" children=[#<Nokogiri::XML::Text:0x3fdce3f781f4 "bar">]>
#<Nokogiri::XML::Text:0x3ffa4e15335c "\n">

document_without_blanks.root.children.each { |child| p child }
#<Nokogiri::XML::Element:0x3f81bef42034 name="bar" children=[#<Nokogiri::XML::Text:0x3f81bef43ee8 "bar">]>

The NOBLANKS shouldn't remove empty nodes:

doc = Nokogiri.XML('<foo><bar></bar></foo>') do |config|
  config.noblanks
end

doc.root.children.each { |child| p child }
#<Nokogiri::XML::Element:0x3fad0fafbfa8 name="bar">

As OP pointed out the documentation on the Nokogiri website (and also on the libxml website) about the parser options is quite cryptic, following a specification of the behaviour ot the NOBLANKS option:

require 'rspec/autorun'
require 'nokogiri'

def parse_xml(xml_string)
  Nokogiri.XML(xml_string) { |config| config.noblanks }
end

describe "Nokogiri NOBLANKS parser option" do

  it "removes whitespace nodes if they have siblings" do
    doc = parse_xml("<root>\n <child></child></root>")
    expect(doc.root.children.size).to eq(1)
    expect(doc.root.children.first).to be_kind_of(Nokogiri::XML::Node)
  end

  it "doesn't remove whitespaces nodes if they have no siblings" do
    doc = parse_xml("<root>\n </root>")
    expect(doc.root.children.size).to eq(1)
    expect(doc.root.children.first).to be_kind_of(Nokogiri::XML::Text)
  end

  it "doesn't remove empty nodes" do
    doc = parse_xml('<root><child></child></root>')
    expect(doc.root.children.size).to eq(1)
    expect(doc.root.children.first).to be_kind_of(Nokogiri::XML::Node)
  end

end
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男人必须洒脱
4楼-- · 2019-06-16 05:04

Nokogiri's noblanks config option doesn't remove all whitespace Text nodes when they have siblings:

describe "Nokogiri NOBLANKS parser option" do

  it "doesn't remove whitespace Text nodes if they're surrounded by non-whitespace Text node siblings" do
    doc = parse_xml("<root>1 <two></two> \n <three></three> \n <four></four> 5</root>")
    children = doc.root.children

    expect(children.size).to_not eq(5)
    expect(children.size).to eq(7)  #Because the two newline Text nodes are not ignored
    expect(doc.root.children.first).to be_kind_of(Nokogiri::XML::Node)
  end
end

I'm not sure why Nokogiri was programmed to work that way. I think it would be better to either ignore all whitespace Text nodes are don't ignore any Text nodes.

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