til/rails/prevent-mailer-previews-from-cluttering-database.md

Prevent Mailer Previews From Cluttering Database

ActionMailer Previews give you a way to view email templates that your system sends. This is how I check that it is styled properly and that the logic and data of the template are able to run and render.

Data for a preview typically means we need ActiveRecord objects and even their associations. If we start creating one-off records in our previews either with #create or with something like FactoryBot, those records will get left behind in our development database. Every view and refresh of a preview will generate more of these records.

One way to get around that is to use #new and #build. I've found this cumbersome and it often leaves assocations missing or inaccessible.

What if instead the preview could clean up after itself? That sounds like a great job for a database transaction.

Let's create a test/mailers/previews/base_preview.rb as a base class for all our preview classes.

class BasePreview < ActionMailer::Preview
  def self.call(...)
    message = nil
    ActiveRecord::Base.transaction do
      message = super(...)
      raise ActiveRecord::Rollback
    end
    message
  end
end

This wraps the existing self.call functionality in a transaction that collects the resulting message from the preview and then rolls back the database changes.

Now, instead of our individual preview classes inheriting directly from ActionMailer::Preview, they can inherit from BasePreview.

class UserMailer < BasePreview

  # ...

end

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