Added reactive version of customer service. #1

dartartem · 2021-04-28T17:20:30Z

No description provided.

cer · 2021-04-28T17:30:17Z

...in/java/io/eventuate/examples/tram/ordersandcustomers/customers/service/CustomerService.java

+
+    return customerRepository
+            .save(customerWithEvents.result)
+            .flatMap(customer -> domainEventPublisher.publish(Customer.class, customer.getId(), customerWithEvents.events).collectList().map(messages -> customer))


.map(messages -> customer) -> https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Mono.html#thenReturn-V-

cer · 2021-04-28T17:31:08Z

...in/java/io/eventuate/examples/tram/ordersandcustomers/customers/service/CustomerService.java

+
+    return customerRepository
+            .save(customerWithEvents.result)
+            .flatMap(customer -> domainEventPublisher.publish(Customer.class, customer.getId(), customerWithEvents.events).collectList().map(messages -> customer))


This line is rather long

... .collectList() .map(message

cer · 2021-04-28T17:40:07Z

...main/java/io/eventuate/examples/tram/ordersandcustomers/customers/domain/ReservedCredit.java

+import java.math.BigDecimal;
+
+@Table("reserved_credit")
+public class ReservedCredit {


This should be called CreditReservation and the table credit_reservation(s)

cer · 2021-04-28T17:41:40Z

...main/java/io/eventuate/examples/tram/ordersandcustomers/customers/domain/ReservedCredit.java

+    return id;
+  }
+
+  public void setId(Long id) {


Are setters needed?

cer · 2021-04-28T17:45:19Z

...java/io/eventuate/examples/tram/ordersandcustomers/customers/web/OrderEventHttpConsumer.java

+  }
+
+  @RequestMapping(value = "/events/orderserviceevents/io.eventuate.examples.tram.ordersandcustomers.orders.domain.Order/{aggregateId}/io.eventuate.examples.tram.ordersandcustomers.orders.domain.events.OrderCreatedEvent/{eventId}", method = RequestMethod.POST)
+  public Mono<Void> handleOrderCreatedEvent(@RequestBody OrderCreatedEvent event, @PathVariable("aggregateId") String aggregateId) {


What support is there for handling duplicate events?
e.g. what would happen if the OrderCreatedEvent was delivered twice?

BTW If the primary key of a CreditReservation was (customerId, orderId) this might help

Chris, there is duplicate publishing detection: https://github.com/eventuate-tram/eventuate-tram-messaging-http/blob/master/eventuate-tram-http-spring-consumer/src/main/java/io/eventuate/tram/http/spring/consumer/duplicatedetection/IdempotentHandlerAspect.java

Is it used in the Customer Service?
If so what about the reactive vs. non reactive transaction issue?
This also means that the event handlers should not manage their own transactions.

Chris, I do not understand. Http proxy delivers events to customer service, if event is duplicated it is not delivered to customer service.

but r2dc does not support embedding

Spring Data R2DBC repositories might not support composite primary keys but r2dbc is a reactive library for executing SQL statements. The SQL statements can do what ever you want. This is some very simple database access code for loading/saving CreditReservations.

So, I need to keep spring data for customer, but replace it by sql for reservations, right?

So, I need to keep spring data for customer, but replace it by sql for reservations, right?

What are the options and their respective trade-offs. Which one do you think is best?

Other option is to completely remove spring data. it has only one advantage: more consistent approach. However, I think it is ok to use simple high-level approach where it is possible and lower-level sql where it is not.

Please file an issue to remove pointless duplicate key detection from the HTTP proxy.
Done: eventuate-tram/eventuate-tram-messaging-http#13

cer · 2021-04-28T17:48:22Z

...in/java/io/eventuate/examples/tram/ordersandcustomers/customers/service/CustomerService.java

+
+  public Mono<Void> reserveCredit(long orderId, long customerId, Money orderTotal) {
+
+    Mono<Customer> possibleCustomer = customerRepository.findById(customerId);


This doesn't handle the scenario where there are two simultaneously attempts to reserve credit.
Both will read existing and potentially exceed the available credit.

This might be a bug in the existing customer service BTW. The solution would be to implement optimistic locking in the Customer.

As I know, optimistic locking works only with single row, but we are reserving credit using separate table. We can use Serializable isolation level. Or probably modify customer to hold a sum of reservations and if insert row to credit_reservation and update the sum in the same transaction, in case if there is concurrent modification, insert will be rolled back together with customer changes. In theory. I need to check docs to recall details about optimistic locking and write a test. Also there could be other useful lock types, for example postgres has Advisory Locks (https://www.postgresql.org/docs/9.1/explicit-locking.html), it could be something similar for mysql, but it definitely would complicate the code.

implement optimistic locking in the Customer

The Customer has a version column, which is incremented whenever a CreditReservation is inserted/deleted.
e.g.

Load Customer to get current version

Insert/delete Credit Reservation

update Customer set version = version + 1 where id = ? and version = <old version>

and if this update will return 0 updated rows, then rollback, right?

Yes. Rollback and retry.

Got it, thank you

cer · 2021-04-28T17:58:07Z

...in/java/io/eventuate/examples/tram/ordersandcustomers/customers/service/CustomerService.java

+    return customerRepository
+            .save(customerWithEvents.result)
+            .flatMap(customer -> domainEventPublisher.publish(Customer.class, customer.getId(), customerWithEvents.events).collectList().map(messages -> customer))
+            .as(transactionalOperator::transactional);


The code should use @Transactional

Chris, as we discussed there are problems with that annotation, and I thought that we decided to use transnational operator

The docs say that @transactional, which is the standard spring mechanism, should work for reactive. Correct?

Therefore, if it's not working in the example application then either the application is incorrect or there is a bug in spring.

ok, I will research

dartartem added 2 commits April 28, 2021 19:37

Added reactive version of customer service.

55d70ea

Changed permissions.

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cer requested changes Apr 28, 2021

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cer merged commit ab469f2 into eventuate-examples:master Apr 28, 2021

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Added reactive version of customer service. #1

Added reactive version of customer service. #1

dartartem commented Apr 28, 2021

cer Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021

cer Apr 28, 2021

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dartartem Apr 28, 2021

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dartartem Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021

dartartem Apr 28, 2021

cer Apr 28, 2021 •

edited

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dartartem Apr 28, 2021


		public Mono<Void> reserveCredit(long orderId, long customerId, Money orderTotal) {

		Mono<Customer> possibleCustomer = customerRepository.findById(customerId);

Added reactive version of customer service. #1

Added reactive version of customer service. #1

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dartartem commented Apr 28, 2021

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cer Apr 28, 2021 • edited Loading

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