Asociaciones many_tomany

referencias:


asociacioes básicas
http://guides.rubyonrails.org/association_basics.html

consulta con mvc
http://stackoverflow.com/questions/11480939/many-to-many-has-many-through-association-form-with-data-assigned-to-linking-m

para las vistas
http://api.rubyonrails.org/classes/ActionView/Helpers/FormHelper.html#method-i-fields_for

ejemplo avanzado
http://www.createdbypete.com/articles/working-with-nested-forms-and-a-many-to-many-association-in-rails-4/

consulta actual Rails 4
http://stackoverflow.com/questions/19473044/rails-4-many-to-many-association-not-working