accepts_nested_attributes

accepts_nested_attributes.rb

class Availability < ActiveRecord::Base
  has_many :availability_periods, dependent: :destroy, inverse_of: :availability
  accepts_nested_attributes_for :availability_periods, allow_destroy: true
  validates_associated  :availability_periods
  validate :must_have_periods

  def must_have_periods
    if availability_periods.empty? or availability_periods.all? {|period| period.marked_for_destruction? }
      errors.add(self.property.name, I18n.t('models.availability.periods_required'))
    end
  end
end

class AvailabilityPeriod < ActiveRecord::Base
  belongs_to :availability, inverse_of: :availability_periods
  validates :date_range, :availability, presence: true
end