gistfile1.rb

class Match < Sequel::Model
  validates do
    presence_of :first_player_id
    presence_of :second_player_id
    presence_of :happens_at
    presence_of :sport_id
  end
  
  def validate
    super
    errors.add(:second_player_id, 'Selected teams have to be different.') if first_player_id == second_player_id
  end
end