1. has_many
vs
has_one
2010/10/02 Shouichi KAMIYA

2. Given
class App ActiveRecord::Base
has_many :servers
end
class Server ActiveRecord::Base
belongs_to :app
end

3. Then
irb> app = App.new
irb > app.servers = [Server.new]
irb > app.servers
#=> [#<Server:0x101141d68>]

4. Looking good.

5. Given
class App ActiveRecord::Base
has_one :server
end
class Server ActiveRecord::Base
belongs_to :app
end

6. Then
irb> app = App.new
irb > app.server = Server.new
irb > app.server
#=> nil

7. What!?

8. The correct way
irb> app = App.new
irb > app.set_server_target = Server.new
irb > app.server
#=> #<Server:0x101141d68>

9. WTF...
Thanks!