Need explanation on the necessity of a prior flushing to avoid false positives whenTesting with Spring ?

Question

In the spring documentation regarding testing, it states:

Avoid false positives when testing ORM code

When you test code involving an

Answer 1

Annotating Spring tests with @Transactional is convenient but it's not how your production code will be executed. The @Transactional annotation will start a transaction prior to running your test method and it will roll it back when the test method finishes.

While commit is preceded by a flush, the roll-back is not, so a manual flush is a safety-mechanism to ensure all Entity changes are translated to SQL statements.

A more appropriate design would be to draw the transaction boundaries explicitly like this:

@Test
public void testRootObjects() {

    final Company newCompany = new Company();
    newCompany.setName("TV Company");

    final Long companyId = transactionTemplate.execute(new TransactionCallback() {
        @Override
        public Long doInTransaction(TransactionStatus transactionStatus) {
            entityManager.persist(newCompany);
            return newCompany.getId();
        }
    });
    Company detachedCompany = transactionTemplate.execute(new TransactionCallback() {
        @Override
        public Company doInTransaction(TransactionStatus transactionStatus) {
            Company attachedCompany = entityManager.find(Company.class, companyId);
            assertEquals(newCompany, attachedCompany);
            assertEquals(newCompany.hashCode(), attachedCompany.hashCode());
            return attachedCompany;
        }
    });
    assertEquals(newCompany, detachedCompany);
    assertEquals(newCompany.hashCode(), detachedCompany.hashCode());
}

The TransactionTemplate will commit your code so there's no need for manual flushes.

If you call @Transactional service methods through their interface, you won't need the transactionTemplate at all, since you are calling a Spring proxy which will call TransactionInterceptor (assuming you instructed Spring to be aware of transaction annotations: ) and therefore transactions will be started/committed on your behalf.