dm-mapped_property.rb

module MappedProperty
  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods
    def mapped_property(name, geocoder = "Location")
      class_eval <<-END, __FILE__, __LINE__
        property :#{name}, String
        property :#{name}_lng, Float
        property :#{name}_lat, Float
        property :#{name}_country, String
        property :#{name}_state, String
        property :#{name}_city, String
        def #{name}=(val)
          attribute_set(:#{name}, val)
          self.#{name}_lng = self.#{name}_lng = self.#{name}_country = self.#{name}_state = self.#{name}_city = nil
          begin
            g = #{geocoder}.geocode(val)
            if g
              self.#{name}_lng = g.lng
              self.#{name}_lat = g.lat
              self.#{name}_country = g.country_code
              self.#{name}_state = g.state
              self.#{name}_city = g.city
            end
          rescue
          end
        end
      END
    end
  end
end

geokit_initializer.rb

require 'geokit'
Geokit::Geocoders::google = "YOUR_API_CODE"
Geokit::Geocoders::provider_order = [:google]
GoogleMap = Geokit::Geocoders::GoogleGeocoder

location.rb

class Location
  include DataMapper::Resource
    
  property :id, Serial
  property :name, String, :length => 255, :key => true
  property :geocode, Object

  def self.geocode(val)
    return nil if (val.nil? || val.empty?)
    l = Location.first(:name => val)
    return l.geocode if l
    begin
      g = GoogleMap.geocode(val)
    rescue
    end
    if g
      Location.create(:name => val,:geocode => g)
    end
    g
  end
end