beginning of a DSL for me to abuse embedding and linking in MongoDB

gistfile1.rb

# Facets are little bits of info about visitors

# Each facet has it's own Mongo collection; however,
# Essential attributes of the facet are imbedded in an Impression.

# This greatly improves performance by avoiding extraneous lookups,
# but also links Facets to their respectful impressions, much like
# facet :has_many => :impressions

# The containing module serves to provide "facet definitions" --
# A DSL for creating the essential skeleton of a facet

module Arbiter
  
  class << self
    attr_accessor :facets
  end
  self.facets = []
  
  module Facets
    
    # Meta-magic for the syntactically lip-smacking DSL below
    def self.method_missing(meth, *args, &blk)
      if meth.to_s[/^[A-Z]/]# && args[0] && blk
        colname = args[0]
        
        # Instantiate a new facet class
        eval "#{meth} = Class.new"
        
        # Extend facet class
        class << klass = Kernel.const_get(meth)
          attr_reader :param_keys
          attr_reader :parse_proc
          attr_reader :key
          
          def key(k)
            @key = k
          end
          
          def parse(*k, &proc)
            @param_keys = k
            @parse_proc = proc
          end
          
          # Parse parameter values into Impression-mergeable hash
          def parse_params(params)
            vals = @param_keys.select {|k| params[k] && !params[k].empty? }
            if vals.all?
              { @key => @parse_proc.call(*vals) }
            end
          end
          
        end
        
        # Apply constructor definitions to facet class
        blk.call(klass)
        
        Arbiter.facets << klass
        Collection.register(colname, klass)
      else
        super(meth, *args, &blk)
      end
    end
    
    # Facet Definitions_________________________________________
    Region('regions') do
      key :l
      parse(:ip) do |ip|
        geo = GeoIP.get_location(ip)
        if geo.location
          { :_id => geo.location['_id'], :f => geo.region.f }
        end
      end
    end
  
    Referrer('refs') do
      key :r
      parse do |url|
        ref = @collection.find_or_create('url' => url)
        { :_id => ref.id, :f => ref.url }
      end
    end
  
    ScreenRes('screens') do
      key :sr
      parse(:sx, :sy) do |x, y|
        @collection.find_or_create_from_dim(x, y).id
      end
    end
  
    Agent('agents') do
      key :a
      parse do |raw|
        agent = @collection.find_or_create('raw' => raw)
        { :_id => agent.id, :f => agent.raw }
      end
    end
  
  end
end