Filter Rails SQL log in production

In order to debug a problem, which only occurred in production, we recently wanted to tweak our Rails SQL logs to only show the access to a specific table.

Here’s what we did to accomplish this. We created a file initializers/filter_sql_log.rb with this content:

if Rails.env.production?
  module ActiveRecord
    class LogSubscriber
      alias :old_sql :sql

      def sql(event)
        if event.payload[:sql].include? 'users'
          old_sql(event)
        end
      end
    end
  end
end

This monkey-patches the ActiveRecord::LogSubscriber class and only delegates to the old logging method, if the SQL statement includes the string "users".

By default, SQL logging is deactivated in the Rails production environment. Therefore we needed to change config/environments/production.rb like this:

config.log_level = :debug