Weird exception with delayed_job

Question

Trying to queue a job with delayed_job as follows:

Delayed::Job.enqueue(BackgroundProcess.new(current_user, object))

current_user and object are not nil when I print them out. The weird thing is that sometimes refreshing the page or running the command again works!

Here is the exception trace:

  Delayed::Backend::ActiveRecord::Job Columns (44.8ms)   SHOW FIELDS FROM `delayed_jobs`

TypeError (wrong argument type nil (expected Data)):
  /Users/.rvm/rubies/ruby-1.9.1-p378/lib/ruby/1.9.1/yaml.rb:391:in `emit'
  /Users/.rvm/rubies/ruby-1.9.1-p378/lib/ruby/1.9.1/yaml.rb:391:in `quick_emit'
  /Users/.rvm/rubies/ruby-1.9.1-p378/lib/ruby/1.9.1/yaml/rubytypes.rb:86:in `to_yaml'
  vendor/plugins/delayed_job/lib/delayed/backend/base.rb:65:in `payload_object='
  activerecord (2.3.9) lib/active_record/base.rb:2918:in `block in assign_attributes'
  activerecord (2.3.9) lib/active_record/base.rb:2914:in `each'
  activerecord (2.3.9) lib/active_record/base.rb:2914:in `assign_attributes'
  activerecord (2.3.9) lib/active_record/base.rb:2787:in `attributes='
  activerecord (2.3.9) lib/active_record/base.rb:2477:in `initialize'
  activerecord (2.3.9) lib/active_record/base.rb:725:in `new'
  activerecord (2.3.9) lib/active_record/base.rb:725:in `create'
  vendor/plugins/delayed_job/lib/delayed/backend/base.rb:21:in `enqueue'

Answer 1

I would guess that it is caused by the fact that you send the objects as arguments to your jobs (at least I assume that current_user and object are in fact objects and not id's). Send the id's instead and start with loading the objects when perform starts.

For example:

Delayed::Job.enqueue(BackgroundProcess.new(current_user.id, object.id))

class BackgroundProcess < Struct.new(:user_id, :object_id)
  def perform
    @current_user = User.find(user_id)
    @object = Object.find(object_id)

    ...
  end
end

This way, it does not risk any problem with serializing an ActiveRecord into the database and you will always load the latest changes when the job is run.