In my work on Spree, sometimes I’ve been wanting to know where queries are coming from. Just like any large codebase, the “magic” that goes on inside it to make the cogs spin the right way can be a bit complex.

Active Support’s Notifications feature is really handy for this. All I need to do is subscribe to the sql.active_record event and get it to output the stacktrace of where the query is generated, like this:

ActiveSupport::Notifications.subscribe("sql.active_record") do |_, _, _, _, details|
  if details[:sql] =~ /INSERT INTO "spree_inventory_units"/
    puts caller.join("\n")
    puts "*" * 50

Whenever a query that inserts a new record into the spree_inventory_units table is issued through Active Record, this code will give me a complete stacktrace of where that came from.