ticket.rb

class Ticket < ActiveRecord::Base
  belongs_to :grouper
  belongs_to :user

  validate :user_cant_be_blacklisted, on: :confirmation
  validate :user_cant_double_book, on: :confirmation

  validate :grouper_cant_be_full, on: :confirmation
  validate :grouper_cant_have_occurred, on: :confirmation

  validate :ticket_cant_have_been_confirmed, on: :confirmation


  def confirm
    update confirmed: true if confirmable?
  end
  
  def confirmable?
    valid? :confirmation
  end

  
  private
    def user_cant_be_blacklisted
      errors.add :user, "can't book a Grouper at this time" if user.blacklisted?
    end
    
    def user_cant_double_book
      errors.add :user, 'are already going to a Grouper on that day' if user.has_existing_grouper?(grouper)
    end
    
    def grouper_cant_be_full
      errors.add :grouper, 'has already occurred!' if grouper.full?
    end
    
    def grouper_cant_have_occurred
      errors.add :grouper, 'has already occurred!' if grouper.past?
    end
    
    def ticket_cant_have_been_confirmed
      errors.add :user, 'have already confirmed this ticket' if confirmed?
    end
end

I didn't know that this is possible and judging from all the if: or unless: constructs I'm obviously not the only one. It's a pity though that I can't pass an array to the on: or context: option. Is this intended?

David, how would you handle the logic in the controller which sets the redirect based on the error message? I think to couple the controller code to the message text is not optimal, in case one changes the message text. I suppose one could define constants for these, and go off of the constants. And then the question is whether the controller should have all the logic pairing up the specific error message with the right redirect. I would tend to write code directly in the controller at first, and then refactor into a separate class where I could verify the logic separate from the actual controller, per my example here: shakacode/fat-code-refactoring-techniques#6

I wish there was an :except_on. I want to validate association presence except in tests, where I don't want to necessarily create a huge object graph just to test some isolated functionality. My strategy has been to use an attr_accessor to set :skip_association_presence_validations in tests. I wish I could use contexts.