gistfile1.rb

class Location
  include Mongoid::Document
  include Geocoder::Model::Mongoid
  
  field :user_defined_location
  field :lat, :type => Float
  field :lon, :type => Float
  field :coords, :type => Array
  index :coords
  
  ...
  
  geocoded_by :user_defined_location, :coordinates => :coords, :latitude => :lat, :longitude => :lon
  
  reverse_geocoded_by :coords do |location, results|
    if geo = results.first
      location.lat                    = geo.latitude
      location.lon                    = geo.longitude
      location.coords                 = geo.coords
    end
  end
  
  after_validation :geocode, :reverse_geocode,
    :if => lambda{ |obj| obj.user_defined_location_changed? }
end