Question

I have a form that students are using to rank 6 classes from 1 to 6. If they select Math as “1” (the hardest), then I don’t want them to be able to select another subject as the hardest. The form will obviously give them the option to select “1” for each subject, but I want to use validations to protect against submission of a form that doesn’t follow instructions

This is a snippet from the form

<div class="field">
    <%= f.label(:math, "Mathp") %>
    <%= f.select:math, 1..6 %> </br>
    </div>

<div class="field">
    <%= f.label(:french, "French") %>
    <%= f.select:french, 1..6 %> </br>
    </div>

I was going to use a validation method like this, but I don’t think the logic of it works (i.e. it doesn’t guard against every possible situation) and it’s probably shitty (non-functional) code too, because i’m just learning how to code (actually I’ve been failing at it for quite a while now). Can you suggest improvements?

validates :rank_favorites 


...

def rank_favorites

unless :math != :french && :french != :history && :history != :spanish && :spanish != :art && :art != :physed return false

end

Answer 1

Your rank_favorites is, sadly, way off but ignorance can be fixed through learning. You’re just comparing a bunch of symbols and that doesn’t do anything useful (at least not as far as you’re concerned), you’re validator reduces to this:

unless false && false && false && false && false return false

which is equivalent to:

unless false return false

You probably want to use validate :rank_favorites (not validates) and your validator would add error messages instead of simply return a boolean:

validate :rank_favorites

#...

def rank_favorites
  ranks = [math, french, history, spanish, art, physed]
  if(ranks.include?(nil))
    errors[:base] << 'Rank all of them you lazy person!'
  elsif(ranks.uniq.length != ranks.length)
    errors[:base] << 'You fail at ranking, no duplicates allowed.'
  end
end

The Array#uniq method will produce a copy of your array with the duplicates removed, if the lengths don’t match then something was removed and you had duplicate entries.

You might want to spend some time reading the validations guide:

Active Record Validations and Callbacks