How to add a new node to XML - ruby

Question

I have a simple XML file, items.xml:
<?xml version="1.0" encoding="UTF-8" ?>
<items>
<item>
<name>mouse</name>
<manufacturer>Logicteh</manufacturer>
</item>
<item>
<name>keyboard</name>
<manufacturer>Logitech - Inc.</manufacturer>
</item>
<item>
<name>webcam</name>
<manufacturer>Logistech</manufacturer>
</item>
</items>
I am trying to insert a new node with the following code:
require 'rubygems'
require 'nokogiri'
f = File.open('items.xml')
#items = Nokogiri::XML(f)
f.close
price = Nokogiri::XML::Node.new "price", #items
price.content = "10"
#items.xpath('//items/item/manufacturer').each do |node|
node.add_next_sibling(price)
end
file = File.open("items_fixed.xml",'w')
file.puts #items.to_xml
file.close
However this code adds a new node only after the last <manufacturer> node, items_fixed.xml:
<?xml version="1.0" encoding="UTF-8"?>
<items>
<item>
<name>mouse</name>
<manufacturer>Logitech</manufacturer>
</item>
<item>
<name>keyboard</name>
<manufacturer>Logitech</manufacturer>
</item>
<item>
<name>webcam</name>
<manufacturer>Logitech</manufacturer><price>10</price>
</item>
</items>
Why?

Answer 1

It would be helpful to distinguish between a Node (a particular piece of structured XML data at a particular place in a tree), and a "node template" which is the structure of the data.
Nokogiri (and most other XML libraries) only allow you to specify Nodes, not node templates. So when you created price = Nokogiri::XML::Node.new "price", #items, you had a particular piece of data that belongs in a particular place, but hadn't defined the place yet.
When you added it to the first <item>, you defined its place. When you added it to the second <item>, you uprooted it from its place and put it in a new place. At that point this Node appeared only in the second <item>. This continues when you add the same Node to each item, until you reach the last <item>, which is where the node stays.
Nokogiri doesn't have any way to specify a node template. What you need to do is:
#items.xpath('//items/item/manufacturer').each do |node|
price = Nokogiri::XML::Node.new "price", #items
price.content = "10"
node.add_next_sibling(price)
end

Answer 2

I'd start with this:
require 'nokogiri'
doc = Nokogiri::XML(<<EOT)
<?xml version="1.0" encoding="UTF-8"?>
<items>
<item>
<name>mouse</name>
<manufacturer>Logitech</manufacturer>
</item>
<item>
<name>keyboard</name>
<manufacturer>Logitech - Inc.</manufacturer>
</item>
</items>
EOT
doc.search('manufacturer').each { |n| n.after('<price>10</price>') }
Which results in:
puts doc.to_xml
# >> <?xml version="1.0" encoding="UTF-8"?>
# >> <items>
# >> <item>
# >> <name>mouse</name>
# >> <manufacturer>Logitech</manufacturer><price>10</price>
# >> </item>
# >> <item>
# >> <name>keyboard</name>
# >> <manufacturer>Logitech - Inc.</manufacturer><price>10</price>
# >> </item>
# >> </items>
It's easy to build upon this to insert different values for the price.