Question

I recently found out about ActiveSupport::Notifications. I think it’s a great tool to monitor your applications.

I am currently using it outside of Rails to monitor my Sinatra app and it’s working great.

However I use it a lot, to instrument custom queries and would like to somehow notify the result of a query:

my_input = "some_query"
ActiveSupport::Notifications.instrument("myapp.create", :input => my_input) do
  #stuff
  result = search_for my_input
  #stuff
  result
end

Now I can subscribe to this and can also get the query that was executed (which is available in the payload hash). But I would also like to see the result in my subscriber.

So is there a way to add any custom value to the payload while I am executing the block?

Answer 1

Just stumbled upon your question when I was looking for the same thing.

You can simply pass in a block variable, it will represent your payload to you, and you can fill it up while you’re in the block

my_input = "some_query"
ActiveSupport::Notifications.instrument("myapp.create", :input => my_input) do |instrument|
  #stuff
  result = search_for my_input
  instrument[:my_result] = result
  #stuff
  result
end

In your subscriber create a new event from the passed argument:

ActiveSupport::Notifications.subscribe("myapp.create") do |*args|
  event = ActiveSupport::Notifications::Event.new(*args)
  Rails.logger.info event.payload
end