How to use Application Helpers in Ruby on Rails

Question

I'm attempting to post a random testimonial on each page of a site.

I started off by using an application helper like this:

module ApplicationHelper

  def random_testimonial
    @random_testimonial = Testimonial.find(:first, :offset => rand(Testimonial.count))
  end

end

In my view I can reference the method but it's being called on each reference, which makes sense.

I'd like this to be called once on each page view exposing a Testimonial object I can use within the view.

What should I be looking for to do this?

Scott Miller · Accepted Answer · 2009-01-25 05:31:20Z

50

While that works, and I have certainly been known to do this, it violates the MVC separation of concerns. View helpers are not supposed to contain controller/model type logic, which this does.

You might consider refactoring this back into the application controller. Helpers are supposed to be for view formatting and stuff, more than as a function (which is what I kept wanting to do when I got started.)

If you got back into your Testimonail model, do could do

def self.random
  Testimonial.find(:first, :offset => rand(Testimonial.count))
end

then in your application controller, you could do:

def random_testimonial
  @random_testimonial ||= Testimonial.random
end

and call it from a before_filter

This has the advantage of moving the database logic back into the model where it belongs.

answered Jan 25, 2009 at 5:31

Scott Miller

2,3083 gold badges21 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Milan Novota Over a year ago

Agreed. Voted up your solution, Scott. Chris, I'd recommend you to select Scott's answer as a correct one. I was too focused on the problem of caching the variable and missed this obvious flaw in the design.

sunwukung Over a year ago

This is really old I know, but this isn't correct. The View in MVC can QUERY the model, it just can't MANIPULATE it. View Helpers, therefore, can inquire the model state independently of controllers.

Dan Over a year ago

@sunwukung Actually this post is correct. Too often Rails VIEW helpers become a dumping ground for procedural business logic. The point here is SOC. The view should not be instantiating models, nor should it contain model behaviour.

sunwukung Over a year ago

@azriel - neither of which I'm suggesting. The role of view helpers is formatting, as stated - but the V in MVC is permitted to 'observe' the model, and as such can make queries (not updates) on the model to achieve this. Folks see the C as the fence between the M and the V

Dan Over a year ago

@sunwukung This is not querying the model's state. It is creating a new instance of the model based on some business logic. In fact, in the original code, the view is determining the state of the model.

Milan Novota · Accepted Answer · 2009-01-25 04:06:13Z

6

If I understand you correctly, you want a method that returns the same object every time it is referenced in one request/response cycle. If this is true, you can achieve it with a minor change to your helper:

 def random_testimonial
    @random_testimonial ||= Testimonial.find(:first, :offset => rand(Testimonial.count))
 end

Notice the "||=" part. That's a Ruby idiom which says: assign a value to @random_testimonial, unless it already has a value.

Hope that answers your question.

edited Jan 25, 2009 at 4:06

answered Jan 25, 2009 at 3:47

Milan Novota

15.6k7 gold badges57 silver badges62 bronze badges

Collectives™ on Stack Overflow

How to use Application Helpers in Ruby on Rails

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related