Monkey patch PG::Connection to get more a descriptive error message

pg_log_unable_to_send.rb

require 'pg'

class PG::Connection
  def self.wrap_send_method(meth)
    alias_method "#{meth}_wo_wrap", meth

    define_method(meth) do |*args|
      begin
        send("#{meth}_wo_wrap", *args)
      rescue PG::UnableToSend => e
        raise e, "#{e} previous command was #{@last_cmd.inspect}"
      end
      @last_cmd = [meth, args, caller]
    end
  end

  def self.wrap_send_methods(*args)
    args.each { |meth| wrap_send_method(meth) }
  end

  wrap_send_methods :send_query, :send_prepare, :send_query_prepared,
      :send_describe_prepared, :send_describe_portal,
      :exec, :exec_params, :exec_prepared, :async_exec, :query,
      :prepare, :describe_prepared
end

if $0 == __FILE__
  conn = PGconn.new
  conn.send_query("select 1")
  conn.send_query("select 2")

  # $ ruby pg_log_unable_to_send.rb 
  # pg_log_unable_to_send.rb:11:in `rescue in block in wrap_send_method': another command is already in progress (PG::UnableToSend)
  # previous command was [:send_query, ["select 1"], ["pg_log_unable_to_send.rb:29:in `<main>'"]]
  #        from pg_log_unable_to_send.rb:8:in `block in wrap_send_method'
  #        from pg_log_unable_to_send.rb:30:in `<main>'

end