ActionMailer::Preview uses different execution of mailer for email info bar and email content

[barnett]

Steps to reproduce

Create a mailer:

class ObjectMailer < ApplicationMailer
  def event_happened
    @object = Object.new
    mail to: 'test@gmail.com', subject: "#{@object} Happened!"
  end
end

Create a preview:

# Preview all emails at http://localhost:3000/rails/mailers/account_mailer
class ObjectMailerPreview < ActionMailer::Preview
  def event_happened
    ObjectMailer.event_happened
  end
end

And in apps/views/object_mailer/event_happened.html.erb:

<p>@object</p>

The object will differ.

Example Repo

1. Start server
2. Go to /rails/mailers/object_mailer/event_updated
3. 💥

Expected behavior

I would expect the render for the email and email info bar use the same execution. Thus the Object#id in the subject and within the email would be the same.

Actual behavior

They render with different instances.

System configuration

Rails version: 5.0.0.beta1
Ruby version: 2.3.0

[vipulnsward]

The email content is displayed in an iframe and fetched in a separate request(based on whether html or text is selected in dropdown).

cc @pixeltrix if we are interested to update this header info as well. It would need a full-page reload/or not using this iframe though.

[pixeltrix]

Yeah, we'd need to redesign the page so that the whole page would be re-rendered at the same time.

@barnett your example is very contrived - do you have a real-world example where this has affected you?

[barnett]

@pixeltrix sure!

In a PreviewMailer I am using Array#sample to select an Account instance that's in a specific state. The issue is, the body of the mailer will mention one Account, when the subject will mention another (since I have dynamic content in those areas based on the Account).

code sample:

class AccountMailerPreview < ActionMailer::Preview
  def upcoming_surveys
    accounts = Account.active.with_upcoming_surveys
    AccountMailer.upcoming_surveys(accounts.sample.id)
  end
end

While I could hypothetically use Array#first instead of Array#sample, but I like making sure I handle any possible edge cases by randomly choosing one.

[stale]

This issue has been automatically marked as stale because it has not been commented on for at least three months.
The resources of the Rails team are limited, and so we are asking for your help.
If you can still reproduce this error on the 5-1-stable branch or on master, please reply with all of the information you have about it in order to keep the issue open.
Thank you for all your contributions.

[dmytro-spivakov]

Reproduced on Rails 7.0.4