How do I debug this 'no method' error in ruby on rails?

Question

I get the following error:

Delayed::Job SomeMailJob# (NoMethodError) "undefined method `subject' for #<YAML::Object:0x2b0a191f4c78>"

This comes from the following code which references the SombMailJob above:

 class SomeMailJob < Struct.new(:contact, :contact_email) 
   def perform
     OutboundMailer.deliver_campaign_email(contact,contact_email)
   end
 end

Here is the mailer:

class OutboundMailer < Postage::Mailer 

  def campaign_email(contact,email)
    subject    email.subject
    recipients contact.email
    from       'me.com>'
    sent_on    Date.today

    body       :email => email
  end

This is the cron task that invokes the mailer:

Contact.all.each do |contact|
  email = contact.email_today #email_today is a contact method returning email object if <= today

  unless contact.email_today == "none" || email.nil?
    puts "contact info inside cron job"
    puts contact.first_name
    puts email.days
    puts contact.date_entered
    puts contact.colleagues
    puts "substituted subject:"
    puts email.substituted_subject(contact,contact.colleagues)

    # create the Contact Email object that gets created and sent

    contact_email = ContactEmail.new
    contact_email.contact_id = contact.id
    contact_email.email_id = email.id

    contact_email.subject = email.substituted_subject(contact,contact.colleagues)


    puts contact_email.subject

    contact_email.date_sent = Date.today
    contact_email.date_created = Date.today

    contact_email.body = email.substituted_message(contact, contact.colleagues)

    contact_email.status = "sent" 

    #Delayed::Job.enqueue OutboundMailer.deliver_campaign_email(contact,contact_email)
    Delayed::Job.enqueue SomeMailJob.new(contact,contact_email)

    contact_email.save #now save the record

Question: why am I getting this error? I don't even know what the object is because it is coming up with the code, so I can't really drill-down further to debug.

Answer 1

When you enqueue a delayed job, it serializes the things involved (the class, the name of hte method you're calling on it, the arguments) into YAML so it can pull them out later when running the job and work with them.

It looks like in your case the email argument is not getting deserialized properly from YAML before .subject is called on it.

I've found that delayed_job tends to have trouble serializing/deserializing anything that's not a simple stored ActiveRecord object or primitive type (integer, string). I always try to set things up so my Job objects only take record IDs (integers), then in the perform method I find for the objects there and work with them. This would definitely avoid the trouble you're seeing.