transaction_id_sequence.rb

class TransactionIdSequence < ActiveRecord::Base
  belongs_to :contract

  def next_transaction_id
    TransactionIdSequence.transaction do
      TransactionIdSequence.connection.execute("UPDATE `#{self.class.table_name}` SET  `transaction_id_sequence` = `transaction_id_sequence` + 1 WHERE `id` = #{id}")
      TransactionIdSequence.connection.select_value("SELECT `transaction_id_sequence` FROM  `#{self.class.table_name}` WHERE `id` = #{id}").to_i
    end
  end
end