hour.rb

class Hour < ActiveRecord::Base
  belongs_to :user
  
  validates_with PunchclockValidator #defined in config/initializers/punchclock_validator.rb
  validates_presence_of :role, :message => "can't be blank"
  validates_associated :user
  validates_numericality_of :manual, :allow_nil => true
  validates_presence_of :start_time, :if => :punchcard?
  validates_presence_of :manual, :if => :manual?
end

punchclock_validator.rb

class PunchclockValidator < ActiveModel::Validator
  def validate(record)
    if record.start_time > record.end_time
      record.errors[:base] << "Start time is after end time."
    end
  end
end