instance method transaction

# File activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb, line 542
      def transaction(start_db_transaction = true)
        transaction_open = false
        begin
          if block_given?
            if start_db_transaction
              begin_db_transaction
              transaction_open = true
            end
            yield
          end
        rescue Exception => database_transaction_rollback
          if transaction_open && transaction_active?
            transaction_open = false
            rollback_db_transaction
          end
          raise unless database_transaction_rollback.is_a? ActiveRecord::Rollback
        end
      ensure
        if transaction_open && transaction_active?
          begin
            commit_db_transaction
          rescue Exception => database_transaction_rollback
            rollback_db_transaction
            raise
          end
        end
      end