private List<OrderingConstraint> findOrderingConstraints(List<ConstrainedTransaction> transactions) {
        List<OrderingConstraint> orderingConstraints = new ArrayList<>(1);
        for (ConstrainedTransaction transaction : transactions) {
            for (Class<? extends Transaction> afterThis : transaction.before())
                orderingConstraints.add(new OrderingConstraint(transaction.transaction().getClass(), afterThis));
        }
        return orderingConstraints;
    }
Combines all transactions of the same type to one
vespajlib/src/main/java/com/yahoo/transaction/NestedTransaction.java