Question

In a Ruby on Rails application I am trying to use information from fields that are not associated with the model in validation.

Here is part of the model as an example (the whole model has gotten kinda big):

class Scorecard < ActiveRecord::Base
  belongs_to :course
  belongs_to :user

  validate :attributes_consistency

  def attributes_consistency
    # Executed for all scorecards.  Checks if the user completed the hole attributes correctly
    if ( params[:no_fairways] and any_fairways? and !only_nine? ) or ( params[:no_fairways] and !any_h1_to_h9_score_blank and any_h1_to_h9_fairway? and only_nine? ) or ( params[:no_fairways] and !any_h10_to_h18_score_blank and any_h10_to_h18_fairway? and only_nine? )
      errors.add_to_base("You inidicated that you missed all the fairways, but you also marked one or more fairways in the scorecard.  Either uncheck the fairways mistakenly marked or uncheck the 'No fairways' checkbox.")
    end
    if ( params[:no_girs] and any_girs? and !only_nine? ) or ( params[:no_girs] and !any_h1_to_h9_score_blank and any_h1_to_h9_gir? and only_nine? ) or ( params[:no_girs] and !any_h10_to_h18_score_blank and any_h10_to_h18_gir? and only_nine? )
      errors.add_to_base("You inidicated that you missed all the greens, but you also marked one or more greens in the scorecard.  Either uncheck the marked greens on the scorecard or uncheck the 'No GIRs' checkbox.")
    end
  end # attributes_consistency


  def any_h1_to_h9_score_blank?
    h1_score.blank? or h2_score.blank? or h3_score.blank? or h4_score.blank? or h5_score.blank? or h6_score.blank? or h7_score.blank? or h8_score.blank? or h9_score.blank?
  end
  def any_h10_to_h18_score_blank?
    h10_score.blank? or h11_score.blank? or h12_score.blank? or h13_score.blank? or h14_score.blank? or h15_score.blank? or h16_score.blank? or h17_score.blank? or h18_score.blank?
  end

  def any_h1_to_h9_fairway?
    h1_fairway? or h2_fairway? or h3_fairway? or h4_fairway? or h5_fairway? or h6_fairway? or h7_fairway? or h8_fairway? or h9_fairway?
  end
  def any_h10_to_h18_fairway?
    h10_fairway? or h11_fairway? or h12_fairway? or h13_fairway? or h14_fairway? or h15_fairway? or h16_fairway? or h17_fairway? or h18_fairway?
  end

  def any_h1_to_h9_gir?
    h1_gir? or h2_gir? or h3_gir? or h4_gir? or h5_gir? or h6_gir? or h7_gir? or h8_gir? or h9_gir?
  end
  def any_h10_to_h18_gir?
    h10_gir? or h11_gir? or h12_gir? or h13_gir? or h14_gir? or h15_gir? or h16_gir? or h17_gir? or h18_gir?
  end

So how can I access params from the model?

Answer 1

Don’t let params sneak up to the model. There’s no point of having a controller in that case. Instead, checkout this episode from Railscasts that talks about virtual attributes that do not go into the database but can still be used for validations.

You don’t need a corresponding model attribute for the virtual attributes. Define attributes local to the class such as @no_fairways that hold the state.

class ScoreCard < ActiveRecord::Base
  # define attributes and accessors for both fields
  attr_accessor :no_fairways, :no_girs

  ..
end

Now inside you form, you could just write:

<% form_for @scorecard %>
  <%= f.check_box :no_fairways %>
<% end %>