Spring Boot: H2 Not Actually Retrieving From Database - spring

Question

I'm trying to write a simple Repository test in Spring Boot. The Test code looks like this:
public class UserRepositoryTest {
private final TestEntityManager entityManager;
private final UserRepository userRepository;
#Autowired
public UserRepositoryTest(TestEntityManager entityManager, UserRepository userRepository) {
this.entityManager = entityManager;
this.userRepository = userRepository;
}
#Test
public void test() {
String firstName = "Frank";
String lastName = "Sample";
String email = "frank#example.com";
String username = "frank#example.com";
String password = "floople";
String passwordConfirm = "floople";
RegisterUserRequest registerUserRequest = new RegisterUserRequest(firstName, lastName, email, username, password, passwordConfirm);
User user = new User(registerUserRequest);
user.setSpinsRemaining(0);
userRepository.save(user);
userRepository.setSpinsRemainingToTen();
User found = userRepository.findByUsername(username);
assertThat(found.getSpinsRemaining()).isEqualTo(10);
}
What's I expect to happen is that the new User object is persisted to the database, the row in the database is modified to set spinsRemaining to 10, and then the now-modified row is retrieved from H2 and shoved into a new variable named "found". The "found" variable will point to an instance of a User object with ten spins remaining.
What actually happens is that the "found" variable points to the exact same instance of User that the "user" variable is. In fact, if I modify some property of the "user" variable AFTER persisting it to H2, the resultant "found" object also has the modified property. According to IntelliJ, both "user" and "found" are pointing to the same thing. How is that possible?

Answer 1

Hibernate caches entities inside a transaction in memory ("first level cache"). - Every time it retrieves an entity from database (or when it's asked to do so by the entity id) it will first look for it in cache so you don't have multiple instances of one entity with the same ID.
But in tests it's sometimes useful to have a "fresh" entity as it can uncover bugs in your persistance configuration/code. What you need to do:
Call EntityManager#flush - this will force synchronization of your changes to the database (save method does not guarantee that when called inside a transaction).
Call EntityManager#clear - Hibernate will forget about previous entity instances and will start fetching from DB again.
Alternatively: You can also instruct your Spring repository method to clear entities automatically after a modifying query. - But this will wipe out all entity instances and not only the one you are modifying so it might not be desirable in your application code.