Rails - finding through scope best practices?

Question

In rails, I know it is best to do a find through scope

e.g in questions_controller

def index
  @event = Event.find(params[event_id])
  @question = @event.questions
end

but is it also good practice to then do the same in the show action

def show
  @event = Event.find(params[:event_id])
  @question = @event.questions.find(params[:id])
end

or better to just do a find straight on the Question model without scoping it through the event?

I am curious about that and also doing a similar thing with @question.comments.build vs Comment.new when making a new record without creating a question record at the same time.

thanks

Answer 1

If you are only getting the event to get a question, doing Event.find is unnecessary and causes additional work.

Both of the actions you wrote perform two queries.

Answer 2

As to your first question a few things to keep in mind:

• What if you suddenly need @event in your view?
• What if you want to extend Event.find with some custom logic (i.e. access control)?
• Are there reasons not to go by the Event interface?

Personally I would go for using Event's interface for fetching the question(s) if merely to avoid premature optimization.

As for your second question, @question.comments.build will automatically set the right references in your new structure, so I'd go for that as long as @question is available. (Heck, I'd even consider making a @question.add_comment(..) method to the Question class).

Put in other words, premature optimization is the root of all evil. And loose coupling is good for you.