Can a ReadSideProcessor manage multiple events?

Question

My application needs to manage 3 types of events: creation, edit and deletion. Can I manage all these events with just one ReadSideProcessor? Is there any particular order I should prepare the statements in the prepare method?

Answer 1

Yes, ReadSideProcessor.defineEventHandlers accept a builder which can hold multiple events.

Since all events are unique, the order in which to define them is no important. Think about is as a hashmap(event, view-store logic)

see below,

@Override
public EventHandlers defineEventHandlers(EventHandlersBuilder builder) {
    // when Account created, insert account table;
    builder.setEventHandler(TransactionEvent.AccountCreatedEvent.class, (ev, offset) -> {
        System.out.println("offset ->" + offset);
        BoundStatement st = writeAccount.bind()
                                        .setString("account_id", ev.id)
                                        .setString("name", ev.name);


        BoundStatement stOffset = writeOffset.bind(offset);

        return completedStatements(Arrays.asList(st, stOffset));
    });
    // when Deposit, insert history and update balance
    builder.setEventHandler(TransactionEvent.MoneyDepositedEvent.class, (ev, offset) -> {
        System.out.println("offset ->" + offset);
        BoundStatement historyInsert = writeHistory.bind()
                                                   .setString("account_id", ev.id)
                                                   .setLong("amount", ev.amount)
                                                   .setString("type", "DEPOSIT")
                                                   .setTimestamp("at", toTimestamp(offset));

        BoundStatement accountUpdate = updateAccount.bind()
                                                    .setString("account_id", ev.id)
                                                    .setLong("balance", ev.balance + ev.amount);

        return completedStatements(Arrays.asList(historyInsert, accountUpdate, writeOffset.bind(offset)));
    });

    // when Withdrawal, insert history and update balance
    builder.setEventHandler(TransactionEvent.MoneyWithdrawnEvent.class, (ev, offset) -> {
        System.out.println("offset ->" + offset);
        BoundStatement historyInsert = writeHistory.bind()
                                                   .setString("account_id", ev.id)
                                                   .setLong("amount", ev.amount)
                                                   .setString("type", "WITHDRAWAL")
                                                   .setTimestamp("at", toTimestamp(offset));

        BoundStatement accountUpdate = updateAccount.bind()
                                                    .setString("account_id", ev.id)
                                                    .setLong("balance", ev.balance - ev.amount);

        return completedStatements(Arrays.asList(historyInsert, accountUpdate, writeOffset.bind(offset)));
    });
    return builder.build();
}