From: James Britt <james.britt@...>
Date: 2006-12-30T02:40:18+09:00
Subject: Re: XML - converting from one feed to another (beginner)

rb wrote:
> I'm trying to read an XML feed of products and convert them to a
> different XML feed to upload to Froogle (Google Base).
> 
> How do I read the lines of XML and then rewrite them in the new XML?
> I've started with rexml, but I'm not sure if I'm on the right track.  
> 
> 
> def convert_to_base_xml(xml)
>   # Takes a product XML feed and converts it into one that
>   # is formatted for uploading to Google Base
> 
>   # doc = REXML::Document.new
>   feed = REXML::Document.new(xml)
> 
>   # Create the export XML document
>   doc = REXML:Document.new

You may be better off building the new XML using either direct string 
concatenating, or a lib such as Jim Weirich's Builder (which will help 
ensure the result is proper XML).  Or one of the Ruby RSS libraries. 
(I'd go with populating templates and just make sure the new content is 
correctly escaped.)

The general ides is to loop over the item elements in the source DOM 
(using either REXML or Hpricot), extract the relevant data, and populate 
a new item element in the target XML.  If you have a template for the 
target item element you can stuff in the new content on each pass of the 
loop and append it to the resulting XML.

For example, with Hpricot (which  you can install as a gem):

require 'hpricot'

...


src_dom = Hpricot(source_rss_xml).

src_dom/'//item'.each do |el|
    title     = (item/'title').text
    title_url = (item/'title_url').text
    #  ...
    # Now build the new item element for the target XML
    # and add it to the accumulating content
end



(For REXML it's basically the same, but the XPath invocation is different.)

Some considerations may be time and memory needs; if you are dealing 
with large documents, a pull or stream parser would be better, but it 
can be a bit harder to work with if you are new to it.  But see my 
article in Dr. Dobbs: http://www.ddj.com/184406385

Try the simplest approach first and see if it works, and if works well 
enough.


-- 
James Britt

http://www.rubyaz.org         - Hacking in the Desert
http://www.jamesbritt.com     - Playing with Better Toys