street_lookup.rb

module MTData
  class Base < ActiveRecord::Base
    # MT_DATA_DATABASE should have a connection string to one of the
    # specific databases.
    establish_connection MT_DATA_DATABASE
  end

  class Street < Base
    self.table_name = "street"
  end
end


class StreetLookup
    
  InvalidCity = Class.new(StandardError)
  
  def initialize(city, options = {})
    raise InvalidCity unless @city_database_map[city]
    
    @city               = city
    @street_model       = options[:street_model] || MTData::Street
    @city_database_map  = options[:city_database_map] || CITY_DATABASE_MAP
    @street_field       = options[:street_field] || "street"
  end
  
  def find_by_street_name(street_name)
    @street_model.find_by_sql(
      "SELECT * " +
      "FROM #{@city_database_map[city]}.#{@street_model.table_name} " +
      "WHERE #{@street_field} LIKE '?%'",
      street_name
    )
  end
  
end

CITY_DATABASE_MAP = {
  brisbane: "brisbane",
  perth:    "perth"
}

StreetLookup.new(:brisbane, city_database_map: CITY_DATABASE_MAP).find_by_street_name("george")