gistfile1.rb

$ script/console 
Loading development environment (Rails 2.3.8)
ruby-1.8.7-p299 > country = Country.create :name => "Brasil"
 => #<Country id: 3, name: "Brasil", created_at: "2010-07-23 15:37:58", updated_at: "2010-07-23 15:37:58"> 

ruby-1.8.7-p299 > state = State.create :name => "RJ"
 => #<State id: 2, name: "RJ", country_id: nil, created_at: "2010-07-23 15:38:15", updated_at: "2010-07-23 15:38:15"> 

ruby-1.8.7-p299 > country.states << state
 => [#<State id: 2, name: "RJ", country_id: 3, created_at: "2010-07-23 15:38:15", updated_at: "2010-07-23 15:38:28">] 

ruby-1.8.7-p299 > city1 = City.create :name => "Rio de Janeiro"
 => #<City id: 3, name: "Rio de Janeiro", state_id: nil, created_at: "2010-07-23 15:39:00", updated_at: "2010-07-23 15:39:00"> 

ruby-1.8.7-p299 > city2 = City.create :name => "Niteroi"
 => #<City id: 4, name: "Niteroi", state_id: nil, created_at: "2010-07-23 15:39:16", updated_at: "2010-07-23 15:39:16"> 

ruby-1.8.7-p299 > state.cities << city1
 => [#<City id: 3, name: "Rio de Janeiro", state_id: 2, created_at: "2010-07-23 15:39:00", updated_at: "2010-07-23 15:39:28">] 

ruby-1.8.7-p299 > state.cities << city2
 => [#<City id: 3, name: "Rio de Janeiro", state_id: 2, created_at: "2010-07-23 15:39:00", updated_at: "2010-07-23 15:39:28">, #<City id: 4, name: "Niteroi", state_id: 2, created_at: "2010-07-23 15:39:16", updated_at: "2010-07-23 15:39:30">] 

ruby-1.8.7-p299 > state.cities 
 => [#<City id: 3, name: "Rio de Janeiro", state_id: 2, created_at: "2010-07-23 15:39:00", updated_at: "2010-07-23 15:39:28">, #<City id: 4, name: "Niteroi", state_id: 2, created_at: "2010-07-23 15:39:16", updated_at: "2010-07-23 15:39:30">] 

ruby-1.8.7-p299 > country.states
 => [#<State id: 2, name: "RJ", country_id: 3, created_at: "2010-07-23 15:38:15", updated_at: "2010-07-23 15:38:28">] 

ruby-1.8.7-p299 > city1.state
 => #<State id: 2, name: "RJ", country_id: 3, created_at: "2010-07-23 15:38:15", updated_at: "2010-07-23 15:38:28"> 

ruby-1.8.7-p299 > state.country
 => #<Country id: 3, name: "Brasil", created_at: "2010-07-23 15:37:58", updated_at: "2010-07-23 15:37:58"> 

ruby-1.8.7-p299 > exit