Question

I would like to execute a simple sql line each time a new connection is made (on that same connection)

Why?
Using postgres, “set application_name = ‘abc’;” will allow me to keep track of the application using the connections when I query my database server for stats.

Haven’t seen anything that would allow me to do this.

Answer 1

I solved a similar problem recently. I was changing the transaction isolation level after connecting. This example should help you out. It is based on the advice in the final example on this blog post.

# lib/active_record/application_name.rb
module ActiveRecord
  module ApplicationName
    def self.included(base)
      unless base.respond_to? :establish_connection_with_application_name
          base.extend ClassMethods
          base.class_eval do
            class << self
              alias_method_chain :establish_connection, :application_name
            end
          end
      end
    end

    module ClassMethods
      def establish_connection_with_application_name(*args)
        result = establish_connection_without_application_name(*args)
        ::ActiveRecord::Base.connection.execute("set application_name = 'abc';")
        result
      end
    end
  end
end

# lib/patches/active_record.rb
require 'active_record/application_name'

class ActiveRecord::Base
  include ActiveRecord::ApplicationName
end


# config/initializers/patches.rb
require 'patches/active_record'