Why does getOne(…) on a Spring Data repository not

问题:

I'm working on a weird issue, I was doing integration testing, calling my controller to get an object from database that doesn't exist.

public Optional<T> get(Long id) {

  try {
    return Optional.ofNullable(repository.getOne(id));
  } catch(EntityNotFoundException e) {
    return Optional.empty();
  }
}

When getOne(…) is not able to find anything, I was expecting an EntityNotFoundException but actually nothing. If I inspect my result I can see that I have an empty entity with a handler link to it "threw EntityNotFoundException" but we don't go in the catch and I return an optional of this weird entity.

I can't understand this behavior.

回答1:

This is due to the way JPA specifies EntityManager.getReference(…) to work. It's supposed to return a proxy that will either resolve the object to be returned on the first access of a property or throw the contained exception eventually.

The easiest way to work around this is to simply use findOne(…) instead, like this Optional.ofNullable(repository.findOne(…)). findOne(…) will return nullin case no result is found.

A more advanced way of resolving this is to make the repository return Optional instances directly. This can be achieved by creating a custom base repository interface using Optional<T> as return type for the find…-methods.

interface BaseRepository<T, ID extends Serializable> extends Repository<T, ID> {

  Optional<T> findOne(ID id);

  // declare additional methods if needed
}

interface YourRepository extends BaseRepository<DomainClass, Long> { … }

Find a complete example of this in the Spring Data examples repository.

回答2:

This is how it worked for me

public User findUserById(Long id) {
    return userRepository.findById(id).orElse(null);
}