[Rails 6] Advice for injecting manual connection switching for unsubscribe GET route

[rromanchuk]

https://edgeguides.rubyonrails.org/active_record_multiple_databases.html#using-manual-connection-switching

Using Rails 6 multiple database support, the GET request attempts to use the reader role which then fails. Thinking about what the cleanest approach to wrapping opt_out(options) inside of a ActiveRecord::Base.connected_to(role: :writing) block. Right now i'm just monkey patching the controller action.

Similar issues in other gems heartcombo/devise#5133

[ankane]

Hey @rromanchuk, you should be able to add an around_action for the controller in an initializer. Something like:

Mailkick::SubscriptionsController.around_action do
  ActiveRecord::Base.connected_to(role: :writing) do
    yield
  end
end

Another approach could be customizing the resolver to exclude Mailkick paths.

The automatic connection switching feature is opt-in and pretty basic right now (by design), so I don't think it make sense to add official support for it.

[kevinzwhuang]

For anyone reading this and adding an around_action to an initializer, I found that this works:

# config/initializers/mailkick.rb

Mailkick::SubscriptionsController.around_action do |_controller, action|
  ActiveRecord::Base.connected_to(role: :writing) do
    action.call
  end
end

This is because calling around_action inline does not make yield available.
The Rails docs explain that using around_action directly this way gives a controller and an action argument to the block. We can use the action block to yield.

Rails docs explanation: https://guides.rubyonrails.org/action_controller_overview.html#other-ways-to-use-filters
Rails GitHub issue that explains this in more detail: rails/rails#37616