JPA EntityManager not working when using Guice's PrivateModule

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Óscar Andrés López

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Mar 17, 2021, 6:20:05 AM3/17/21
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Hi, this is a crosspost from a question originally asked on Stack Overflow, I thought I might get better results here. Copying verbatim:

I have a service with a persistence setup using JPA, Hibernate and Guice (if it's useful, I'm not using Spring). This is the first, working version of my code:

    public class BookDao {
    
        @Inject
        protected Provider<EntityManager> entityManagerProvider;
    
        protected EntityManager getEntityManager() {
            return entityManagerProvider.get();
        }
    
        @Transactional
        public void persist(Book book) {
            getEntityManager().persist(book);
        }
    
    }
    
    public class MyAppModule extends AbstractModule {
    
        @Override
        protected void configure() {
            initializePersistence();
        }
    
        private void initializePersistence() {
            final JpaPersistModule jpaPersistModule = new JpaPersistModule("prod");
            jpaPersistModule.properties(new Properties());
            jpaPersistModule.configure(binder());
            install(jpaPersistModule);
        }
    
    }

But now I need to configure multiple persistence units. I'm following the advice in this mailing list, and according to them, I should move my module logic to a private module. I did as suggested and created a second version of the same code, the changes are commented below:

     @BindingAnnotation
    @Retention(RetentionPolicy.RUNTIME)
    @Target({ FIELD, PARAMETER, METHOD })
    public @interface ProductionDataSource {} // defined this new annotation
    
    public class BookDao {
    
        @Inject
        @ProductionDataSource // added the annotation here
        protected Provider<EntityManager> entityManagerProvider;
    
        protected EntityManager getEntityManager() {
            return entityManagerProvider.get();
        }
    
        @Transactional
        public void persist(Book book) throws Exception {
            getEntityManager().persist(book);
        }
    
    }
    
    public class MyAppModule extends PrivateModule { // module is now private
    
        @Override
        protected void configure() {
            initializePersistence();
            // expose the annotated entity manager
            Provider<EntityManager> entityManagerProvider = binder().getProvider(EntityManager.class);
            bind(EntityManager.class).annotatedWith(ProductionDataSource.class).toProvider(entityManagerProvider);
            expose(EntityManager.class).annotatedWith(ProductionDataSource.class);
    
        }
    
        private void initializePersistence() {
            JpaPersistModule jpaPersistModule = new JpaPersistModule("prod");
            jpaPersistModule.properties(new Properties());
            install(jpaPersistModule);
        }
    
    }

The newly annotated EntityManager is being correctly injected by Guice and is non-null, but here's the fun part: some of my unit tests started failing, for example:

    class BookDaoTest {
    
        private Injector injector;
        private BookDao testee;
    
        @BeforeEach
        public void setup() {
            injector = Guice.createInjector(new MyAppModule());
            injector.injectMembers(this);
            testee = injector.getInstance(BookDao.class);
        }
    
        @Test
        public void testPersistBook() throws Exception {
            // given
            Book newBook = new Book();
            assertNull(newBook.getId());
            // when
            newBook = testee.persist(newBook);
            // then
            assertNotNull(newBook.getId()); // works in the first version, fails in the second
        }
    
    }

In the first version of my code the last line above just works: the entity is persisted and has a new id. However, in the second version of my code (using a PrivateModule and exposing an annotated EntityManager from it) the persist() operation doesn't work anymore, the entity is without an id. What could be the problem? I didn't do any other configuration changes in my environment, and I don't see error messages in the logs. Let me know if you need more details.

Óscar Andrés López

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Mar 27, 2021, 4:53:31 PM3/27/21
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I found the solution, it's detailed here. TL;DR: the @Transactional annotation was not being executed in the second version of my code, as a workaround I had to implement transaction management by hand. It seems that I stumbled into a Guice bug?
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