So, while developing an app, I have to use event sourcing to track down all changes to model. The app itself is made using spring framework. The problem I encountered: for example, user A sends a command to delete an entity and it takes 1 second to complete this task. User B, at the same time, sends a request to modify, for example, an entity name and it takes 2 seconds to do so. So my program finishes deleting this entity (persisting an event that says this entity is deleted), and after it another event is persisted for the same entity, that says that we just modified its name. But no actions are allowed with deleted entities. Boom, we just broke the app logic. It seems to me, that I have to put methods that write to database in synchronized blocks, but is there are any other way to handle this issue? Like, I dunno, queuing events? The application is not huge, and not a lot of requests are expected, so users can wait for its request turn in the queue (of course I can return 202 HTTP Status Code to him, but like I said, requests are not resource heavy and there wont be a lot of them, so its unnecessary). So what is the best way for me to use here?
EDIT: Added code to illustrate the problem. Is using synchronized in this case is a good practice or there are other choices?
@RestController
@RequestMapping("/api/test")
public class TestController {
@Autowired
private TestCommandService testCommandService;
@RequestMapping(value = "/api/test/update", method = RequestMethod.POST)
@ResponseStatus(HttpStatus.OK)
public void update(TestUpdateCommand command) {
testCommandService.update(command);
}
@RequestMapping(value = "/api/test/delete", method = RequestMethod.POST)
@ResponseStatus(HttpStatus.OK)
public void delete(Long id) {
testCommandService.delete(id);
}
}
public class TestUpdateCommand {
private Long id;
private String name;
public TestUpdateCommand() {
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
public interface TestCommandService {
void delete(Long id);
void update(TestRegisterCommand command);
}
@Service
public class TestCommandServiceImpl implements TestCommandService {
@Autowired
TestEventRepository testEventRepository;
@Override
@Transactional
public void delete(Long id) {
synchronized (TestEvent.class) {
//do logic, check if data is valid from the domain point of view. Logic is also in synchronized block
DeleteTestEvent event = new DeleteTestEvent();
event.setId(id);
testEventRepository.save(event);
}
}
@Override
@Transactional
public void update(TestUpdateCommand command) {
synchronized (TestEvent.class) {
//do logic, check if data is valid from the domain point of view. Logic is also in synchronized block
UpdateTestEvent event = new DeleteTestEvent();
event.setId(command.getId());
event.setName(command.getName());
testEventRepository.save(event);
}
}
}
@Entity
public abstract class TestEvent {
@Id
private Long id;
public Event() {
}
public Event(Long id) {
this.id = id;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
}
@Entity
public class DeleteTestEvent extends TestEvent {
}
@Entity
public class UpdateTestEvent extends TestEvent {
private String name;
public UpdateTestEvent() {
}
public UpdateTestEvent(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
public interface TestEventRepository extends JpaRepository<TestEvent, Long>{
}
