JPA EntityManager not working when using Guice's PrivateModule

[Óscar Andrés López]

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]

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?