app/models/resource.rb
# frozen_string_literal: true
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