osem-fcy/app/models/resource.rb

# frozen_string_literal: true

# == Schema Information
#
# Table name: resources
#
#  id            :bigint           not null, primary key
#  description   :text
#  name          :string
#  quantity      :integer
#  used          :integer          default(0)
#  conference_id :integer
#
class Resource < ApplicationRecord
  belongs_to :conference
  validates :name, :used, :quantity, presence: true
  validates :used, :quantity, numericality: { greater_than_or_equal_to: 0, only_integer: true }
  validate :used_no_more_than_quantity

  private

  def used_no_more_than_quantity
    errors.add(:used, 'cannot be higher than total quantity') if used.present? && quantity.present? && used > quantity
  end
end