Creating XML nodes using Nokogiri

Question

I am having problems creating nodes and adding them to an XML file:

<mainnode>
    <secnode>
         <data1></data2>
         <data2></data2>
    </secnode>
</mainnode>

I want to be able to add to the file like so:

<mainnode>
    <secnode>
         <data1></data2>
         <data2></data2>
    </secnode>
    <secnode>
         <data1></data2>
         <data2></data2>
    </secnode>
</mainnode>

I am having trouble getting the concept of adding nodes with Nokogiri.

This is my current code:

def openXML
    f = File.open("file.xml")
    doc = Nokogiri::XML(f)
end

def parseXML
    mainnode.name = 'mainnode'
    f = openXML
    temp = Nokogiri::XML::Node.new "secnode", f
    mainnode.add_next_sibling(temp)

end

What concepts am I missing?

I need to be able to add instance variables to <data1> and <data2> but I found the Nokogiri tutorial to not be of much help in this area and have not made it past just adding the <secnode> node as a child of <mainnode>.

Any help is appreciated.

Answer 1

Adding nodes in Nokogiri is a lot easier than you think it is, but your question isn't very clear.

If you want to duplicate an existing node:

require 'nokogiri'

xml = <<EOT
<mainnode>
    <secnode>
         <data1></data2>
         <data2></data2>
    </secnode>
</mainnode>
EOT

doc = Nokogiri::XML(xml)

secnode = doc.at('secnode')
doc.root.add_child secnode.dup
puts doc.to_xml

Which, when run, results in:

<?xml version="1.0"?>
<mainnode>
    <secnode>
         <data1/>
         <data2/>
    </secnode>
<secnode>
         <data1/>
         <data2/>
    </secnode></mainnode>

The funky alignment is the result of appending the intervening text nodes used for indentation. The resulting XML is valid.

If you're adding a different set of nodes, it's still easy:

require 'nokogiri'

xml = <<EOT
<mainnode>
    <secnode>
         <data1></data2>
         <data2></data2>
    </secnode>
</mainnode>
EOT

node_to_add = <<EOT
<secnode>
  <data3 />
  <data4 />
</secnode>
EOT

doc = Nokogiri::XML(xml)

doc.root.add_child node_to_add
puts doc.to_xml

Which outputs:

<?xml version="1.0"?>
<mainnode>
    <secnode>
         <data1/>
         <data2/>
    </secnode>
<secnode>
  <data3/>
  <data4/>
</secnode>
</mainnode>

You can use that as a template:

require 'nokogiri'

xml = <<EOT
<mainnode>
    <secnode>
         <data1></data2>
         <data2></data2>
    </secnode>
</mainnode>
EOT

v1 = 'foo'
v2 = 'bar'
node_to_add = <<EOT
<secnode>
  <data3>#{ v1 }</data3>
  <data4>#{ v2 }</data4>
</secnode>
EOT

doc = Nokogiri::XML(xml)

doc.root.add_child node_to_add
puts doc.to_xml

Which looks like:

<?xml version="1.0"?>
<mainnode>
    <secnode>
         <data1/>
         <data2/>
    </secnode>
<secnode>
  <data3>foo</data3>
  <data4>bar</data4>
</secnode>
</mainnode>

Nokogiri makes it very easy to create nodes to be added by using string representations of the XML or HTML, which it then converts on the fly.

Answer 2

require 'nokogiri'

def parse_xml_file(file_name)
  f = File.read(file_name)
  Nokogiri::XML(f) # do not need variable here; it's the return value of the method
end

def add_element(doc, node_name)
  new_element = Nokogiri::XML::Node.new(node_name, doc)
  new_element.content = "anything"
  doc.root.add_child(new_element)
end

doc = parse_xml_file("sample.xml")
add_element(doc, 'secnode')

puts doc.to_s

Your line mainnode.name = 'mainnode' isn't doing anything and will throw an error; you haven't selected anything from the XML document yet.

You should read up on traversing an XML DOM and selecting nodes. Try this primer: https://blog.engineyard.com/2010/getting-started-with-nokogiri

You say you read the Nokogiri docs, but I'd go back and re-read this, too: http://www.nokogiri.org/tutorials/searching_a_xml_html_document.html

Finally, play around with nokogiri by parsing a doc in IRB and seeing what you can do with it. That's a good way to explore and get a feel for nokogiri.