Thanks for your comment On Tuesday, June 9, 2015 at 10:12:10 PM UTC+3, Ignacio Baca Moreno-Torres wrote: > > We made a similar approach using the client/server version variables. But > we call it version/expectedVersion. > > As explained in stackoverflow > <http://www.google.com/url?q=http%3A%2F%2Fstackoverflow.com%2Fquestions%2F7696764%2Fdoes-gwt-requestfactory-support-implementation-of-optimistic-concurrency-control%2F7697307%237697307&sa=D&sntz=1&usg=AFQjCNEjQwYbtnsepzEPUD0X1zeqCT3jAg> > RF > only sent changes, this forces to have an always-null expectedVersion and > manually copy the getVersion to setExpectedVersion to enable optimistic > locking. BUT! it's critical that the entity be detached when you set the > version (or you detach and merge) because if you set the version on an > attached entity the version is not checked (at least in hibernate). > > Yes, I know about detached entity and setting version to it, in the end of my post I pointed this thing, and I pointed how to set version to attached entity (managed by hibernate).
> OTOH, RF only sent changes to the server so optimistic locking is not > required most of the time. Just for curiosity, why you need optimistic > locking? > Because there is a possibility conflict while saving data and users dont want to lose their data or overrite someone else's data. > > Usually only some operation requires fully transactional/optimistic > locking and in our experience, this operations are better handled using > some kind of command pattern. I.e. sent how-to-update instead of > what-to-set. We used the optimistic locking approach initially because we > try to use RF/Entities/Proxies for everything, but now we use commands for > this situations and versions are not required anymore. Moreover, RF has a > problem when you try to repeat an operation (which is a good idea in > optimistic locking), because if the server side fails in the operations > phase (after validation phase) the client entity gets invalidated, and you > can't sent the entity again. > > Yes, I know about this problem. I have workaround it. Now I test it and I you wish I'll post it here In short, I send to server clone of proxy and always create a new request context which will be fired. 1. get immutable proxy A1 from DB 2. driver.display(A1) 3. user clicks save button 4. make a clone of A1 - A2 5. driver.edit(A2, requestContext) 6. driver.flush() 7. validate(A2) on client 8. requestContext.getRequest().save(A2).fire() 9. in case of exception or server validation failure driver.display(A1) 10. user may fix a problem and try save proxy again > > > > > > On Monday, June 8, 2015 at 11:11:41 PM UTC+2, Anton Mityagin wrote: >> >> >> As all you know RequestFactory does not support optimistic locking. >> >> see details >> https://code.google.com/p/google-web-toolkit/issues/detail?id=6046 >> >> I tried to implement it для RequestFactory + Spring + JPA + Hibernate >> >> I took as a basis the idea proposed by Thomas ( >> http://stackoverflow.com/questions/7696764/does-gwt-requestfactory-support-implementation-of-optimistic-concurrency-control/7697307#7697307 >> ). >> >> As he wrote his idea - pure theory. >> >> @ProxyFor(MyEntity.class) >> interface MyEntityProxy extends EntityProxy { >> String getServerVersion(); >> String getClientVersion(); >> void setClientVersion(String clientVersion); >> … >> } >> >> @Entity >> class MyEntity { >> private String clientVersion; >> @Version private String serverVersion; >> >> public String getServerVersion() { return serverVersion; } >> public String getClientVersion() { return null; } >> public void setClientVersion(String clientVersion) { >> this.clientVersion = clientVersion; >> } >> >> public void patchVersion() { >> serverVersion = clientVersion; >> } >> >> public void shouldPatchVersion() { >> return Objects.equal(serverVersion, clientVersion); >> } >> } >> >> On the server-side we need to use somthing like this to edit >> MyEntityProxy >> public <P extends BaseProxy> P edit(P proxy, RequestContext request) >> { >> P mutableProxy = request.edit(proxy); >> >> if (mutableProxy instanceof MyEntityProxy) >> { >> MyEntityProxy myProxy = (MyEntityProxy)mutableProxy; >> myProxy.setClientVersion(myProxy.getServerVersion()); >> } >> } >> >> On the server-side we need to handle case when clientVersion not equals >> to serverVersion. >> >> I think that if we use EntityManager, we do not have to manually throw an >> exception when the versions are not equal. >> It has to do EntityManager when it tries to save domain object in the >> database. Otherwise a situation may arise when >> an object has been checked, but has not been saved to the database, and >> someone else has save the same object. >> >> I think a good place to make check and patch server version right before >> validating the domain object. >> ServiceLayerDecorator >> public <T> Set<ConstraintViolation<T>> validate(T domainObject) >> >> Unfortunately, not enough simply call MyEntity.patchVersion() >> JPA provider uses internal structures to keep current version of maanged >> object. >> And value of serverVersion does not actually play any role. >> >> We need to use specific JPA provider's API to change a version of managed >> object. >> >> In my case it's Hibernate: >> >> @Override >> public <T> Set<ConstraintViolation<T>> validate(T domainObject) >> { >> >> if (domainObject != null && domainObject instanceof HasVersion<?>) >> { >> MyEntity version = (MyEntity)domainObject; >> >> if (!version.*shouldPatchVersion*()) >> { >> ApplicationContext context = >> ApplicationContextHolderLocator.getHolder().getApplicationContext(); >> EntityManager entityManager = context.getBean(EntityManager.class); >> >> if (entityManager.getDelegate() instanceof SessionImplementor) >> { >> SessionImplementor sess = >> (SessionImplementor)entityManager.getDelegate(); >> EntityEntry entry = >> sess.getPersistenceContext().getEntry(domainObject); >> if (entry != null) >> { >> version.*patchVersion*(); >> LockMode lockMode = entry.getLockMode(); >> *entry.forceLocked(domainObject, >> version.getServerVersion());* >> entry.setLockMode(lockMode); >> } >> } >> } >> } >> >> return super.validate(domainObject); >> } >> >> after this manipulation Hibernate will throws StaleObjectStateException >> as expected if client has edited old version of domain object. >> >> >> There is another way to patch version in domain object: >> >> in the method T find(Class<? extends T> clazz, I id); of entities locator >> detach from persistent context the found domain object >> in the method validate(T domainObject) call method *patchVersion*() and >> try to attach domain object to the persistent context by calling >> entityManger.merge. >> No hibernate dependency, but one more database hit while merging object >> and exceptions may be thrown. >> >> >> Please express an opinion on this implementation. >> >> What are the disadvantages? >> >> -- You received this message because you are subscribed to the Google Groups "Google Web Toolkit" group. 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