saucy/app/models/notification.rb

class Notification < ApplicationRecord
  belongs_to :member

  scope :scheduled_for_today, ->() { where(status: 'scheduled', to_be_sent_on: Date.today) }

  def self.send_scheduled_for_today
    ActiveRecord::Base.transaction do
      ActiveRecord::Base.connection.execute('LOCK members IN ACCESS EXCLUSIVE MODE')

      scheduled_for_today.each do |n|
        n.deliver!
      end
    end
  end

  def deliver!
    # actually send the email.
    NotificationMailer.with(notification: self).send(template).deliver_now!

    update(status: 'sent', sent_at: Time.current)
    # TODO: do something about failures
  end
end