Re: Design suggestion for translations/mappings from xml

On Thu, Nov 27, 2008 at 6:33 PM, Brian Lonsdorf <[e-mail]> wrote:
> Thanks so much for your response!

Glad it helped.

> One enhancement that made me smile was a call to attr_accessor in the
> map method :)

Now *you* got me thinking a little step further. Finally I've had some
spare time,
and came up with this couple enhancements (plus implementing the XML stuff:
parsing using nokogiri, generated the XML by hand):

require 'nokogiri'

module XMLMap
	module ClassMethods
		def set_xml_data property, xpath
			re = %r{\A(/(\w+))+(/@(\w+))?\Z}
			raise "Invalid xpath: #{xpath} for attribute #{property}. Only
simple tags and attrs supported (#{re})" unless xpath =~ re
			(@mappings ||= {})[property] = xpath
		end
		
		def mapped_reader property, xpath
			set_xml_data property, xpath
			self.class_eval {attr_reader property.to_sym}
		end

		def mapped_writer property, xpath
			set_xml_data property, xpath
			self.class_eval {attr_writer property.to_sym}
		end

		def mapped_accessor property, xpath
			set_xml_data property, xpath
			self.class_eval {attr_accessor property.to_sym}
		end

		def from_xml xml
			o = self.new
			doc = Nokogiri.XML(xml)
			@mappings.each do |attr, xpath|
				item = doc.xpath xpath
				unless item.empty?
					o.instance_variable_set "@#{attr}".to_sym, item.inner_text
				end
			end
			o
		end
		
		def mappings
			@mappings
		end
	end
	
	def to_xml	
		xml = Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)}
		self.class.mappings.each do |attr, xpath|
			value = instance_variable_get "@#{attr}"
			continue unless value
			tag, attr = xpath.split("/@")
			tags = tag.split("/")
			h = tags[1..-2].inject(xml) {|h, tag| h[tag]}
			if attr
				h[tags[-1]][:attributes][attr] = value
			else
				h[tags[-1]][:value] = value
			end
		end
		output = ""
		xml.each do |node, data|
			generate_node node, data, output
		end
		output
	end
	
	def generate_node node,data,output		
		value = data.delete(:value)
		attrs = data.delete(:attributes)
		output << "<#{node}"
		if attrs
			attrs.each do |attr, value|
				output << " #{attr}=\"#{value}\""
			end
		end
		if value
			output << ">#{value}</#{node}>"
		elsif !data.empty?
			output << ">"
			data.each do |child_tag, child_data|
				generate_node child_tag, child_data, output
			end
			output << "</#{node}>"
		else
			output << "/>"
		end
	end

	def self.included child
		child.extend ClassMethods
	end
end

The XML stuff ended up a little messy, I'd appreciate any help or
comment there. Usage:

class A
  include XMLMap
  mapped_reader :first, "/root/first"
  mapped_reader :second, "/root/second"
  mapped_accessor :attr, "/root/first/@attr"
end

a = A.from_xml %q{<root><first
attr="the_attr_value">the_first_value</first><second>the_second_value</second></root>}
p a
a.attr = "changed value"
puts a.to_xml

I haven't tested very thoroughly, so there might be a bug or two in
there. Probably you will want to reimplement the to_xml method to use
a proper XML generator.
Any comment about the code or approach appreciated, for sure there's
room for improvement :-)

Regards,

Jesus.