Comma Bug Demo

This is a demo for Comma issue #113

Usage

1. Clone the repository
2. Run rails server -b 0.0.0.0
3. Go to http://localhost:3000/audits.csv
4. Get the error

Optional verification:

1. Update the Gemfile to use version 4.2.0
2. Restart the server and go to http://localhost:3000/audits.csv
3. See it is downloading a CSV as expected

Creating this Demo

This demo was created by following these steps:

Step 1. Create a minimal rails app

$ rails new comma-bug --database=sqlite3 --skip-yarn --skip-action-mailer \
  --skip-active-storage --skip-action-cable --skip-sprockets --skip-spring \
  --skip-listen --skip-coffee --skip-javascript --skip-turbolinks \
  --skip-test --skip-system-test  --skip-bootsnap

Step 2. Add gem dependencies to Gemfile and run bundle

# Gemfile
gem 'comma'
gem 'audited'   # this gem uses polymorphic associations

Step 3. Scaffold a sample model

$ rails g scaffold user name:string email:string
$ rails db:migrate

Step 4. Install audited

$ rails generate audited:install
$ rails db:migrate

Step 5. Update User model

• See app/models/user.rb

Step 6. Create a couple of users

• Go to http://localhost:3000/users

Step 7. Create audits model and controller

• See app/models/audit.rb
• See app/controllers/audits_controller.rb
• See config/routes.rb

Note that the error is caused by this piece of code:

# app/models/audit.rb
class Audit < Audited.audit_class
  comma do
    id
    version
    created_at
    auditable_id
    auditable_type
    action
    user_id
    audited_changes

    # These lines are the ones causing the error
    # - Without them, the CSV generation works
    # - With them, and with comma 4.2.0, the CSV generation works
    auditable identity: 'Auditable name'
    user name: 'User name'
  end
end

Step 8. Download a CSV

• Go to http://localhost:3000/audits.csv
• And get the error Polymorphic association does not support to compute class.