From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2008-11-27T18:16:01+09:00
Subject: Re: Design suggestion for translations/mappings from xml

On Thu, Nov 27, 2008 at 7:00 AM, Brian Lonsdorf <brian@trnsfr.com> wrote:
> Hi, i've got an xml file i'm parsing and creating objects from.
>
> The xml is not named, nor formatted like my objects, so i need to define
> a bunch of mappings/translations.
>
> I'm looking for any design patterns or suggestions people might have to
> elegantly solve this.
>
> xml example:
>
> <HotelDescriptiveContent CurrencyCode="USD" TimeZone="GMT;-06"
> BrandCode="BV" HotelCode="517" HotelName="Americas Best Value Inn and
> Suites - Downtown" Overwrite="true" UnitOfMeasureCode="1">
> <HotelInfo WhenBuilt="2000" HotelStatus="Bookable" HotelStatusCode="1">
> <CategoryCodes>
>  <LocationCategory Code="3"></LocationCategory>
>  <SegmentCategory Code="5"></SegmentCategory>
>  <HotelCategory Code="20"></HotelCategory>
> </CategoryCodes>
> <Description>All the comforts of home conveniently...</Description>
>
>
> object example:
>
> class Hotel
>  attr_accessor :property_name, :brand
> end
>
>
> There's a bunch of other classes and corresponding awkwardly named tags.
>
> It'd be killer if i could do a to_xml as well as from.  But not
> crucial...

Here's a rough idea I though of when reading your email:

module XMLMap
	module ClassMethods
		attr_reader :from_xml, :to_xml
		def map property, xpath_to_value
			(@from_xml ||= {})[xpath_to_value] = property
			(@to_xml ||= {})[property] = xpath_to_value
		end
	end
	
	def to_xml	
		"implement to_xml creating all tags and attrs defined in the to_xml
hash: #{self.class.to_xml.inspect}"
	end
	
	def from_xml xml
		"iterate through all xpaths from from_xml
(#{self.class.from_xml.inspect}) initializing the corresponding ivars"
               # Alternatively you could make this a class method that
returns an initialized instance
	end
	
	def self.included child
		puts "inherited"
		child.extend ClassMethods
	end
end

I haven't implemented the XML stuff, but it should be straightforward
if you limit yourself to simple xpaths. Then you can use it like:

class Test
include XMLMap
map :this, "/root/this/tag"
map :that, "/root/that/@attr"
end

test = Test.new.from_xml
"<root><this><tag>this_value</tag></this><that attr="that_value"/>"
test.to_xml

You could also implement a version of the map method that receives a
hash with all the mappings or whatever.

Hope this helps,

Jesus.