aardbei/app/models/person.rb

class Person < ApplicationRecord
  validates :email, presence: true, uniqueness: true
  validates :first_name, presence: true
  validates :last_name, presence: true
  validates :is_admin, presence: true

  validate :birth_date_cannot_be_in_future

  before_validation :not_admin_if_nil

  def birth_date_cannot_be_in_future
    if self.birth_date > Date.today
      errors.add(:birth_date, "can't be in the future.")
    end
  end

  def not_admin_if_nil
    self.is_admin ||= false
  end
end