Вопрос по ruby-on-rails-3, ruby-on-rails – Когда использовать render против redirect_to при обработке ошибок
when you use
render, you pass the instantiated object
this object, newly created or updated, received some params
when attempting to save the object, validation was triggered and, if unsuccessful, added errors to the current instance
so your object in memory contains validation errors.
either the object is saved and you can get the persisted data from database
or if it's not saved, you can have some information you previously stored in session