'Return a transaction with a specific id.'

def get_transaction(self, transaction_id):

    db_result = self.execute(u'SELECT    *    FROM    transactions    WHERE    trader_id    =    ?    AND    transaction_number    =    ?', (unicode(transaction_id.trader_id), unicode(transaction_id.transaction_number))).fetchone()
    return (Transaction.from_database(db_result, self.get_payments(transaction_id)) if db_result else None)
