Rails ActiveJob CronJob

0readme.md

I had to create some recurring jobs, so I decided to implement a simple CronJob module to work this that.

The CronJob module creates an after_perform callback to reschedule the job at the next_occurence, with the same arguments.

I used https://github.com/siebertm/parse-cron to parse the cron expression.

1CronJob.rb

module CronJob
  extend ActiveSupport::Concern

  included do
    # class_attribute set one different value for each subclasses
    class_attribute :cron_exp

    after_perform do |job|
      # Do you want to reschedule and is there a next occurence ?
      if job.reschedule && job.next_occurence
        # Then perform again at next occurence
        job.class.perform_at_next_occurence(job.arguments, job.next_occurence)
      end
    end
  end

  def next_occurence(time = nil)
    self.class.next_occurence(time)
  end

  def reschedule(value = nil)
    @reschedule = value if !value.nil?
    @reschedule = true if @reschedule.nil?
    @reschedule
  end

  class_methods do
    # Helper to get/set the cron_exp class_attribute
    def cron(value = nil)
      self.cron_exp = value if value
      self.cron_exp
    end

    # Calculate the next occurence from the cron_exp and the given (or current) time.
    def next_occurence(time = nil)
      return if !self.cron
      time ||= Time.now
      CronParser.new(self.cron).next(time)
    end

    def perform_at_next_occurence(arguments, occurence = nil)
      occurence ||= self.next_occurence
      set(wait_until: occurence).perform_later(*arguments)
    end
  end
end

2BackupJob.rb

# Example of how I use it
class BackupJob < ActiveJob::Base
  # Include the module
  include CronJob

  queue_as :backup

  # Specify the cron expression, it's the same as `self.cron_exp = '0 3 * * *'`
  cron '0 3 * * *'

  # The perform method itself could have no arguments, this one is just here to enabled backup on demand
  # without rescheduling a new backup
  def perform(requested = false)
    reschedule !requested # reschedule only if not requested
    # perform backup
  end
end