How to access entity manager with spring boot and spring data

Question

How can I get access to the Entity Manager in the repository when using Spring Boot and Spring Data?

Otherwise, I will need to put my big query in an annotation. I would prefer to have something more clear than a long text.

Answer 1

You would define a CustomRepository to handle such scenarios. Consider you have CustomerRepository which extends the default spring data JPA interface JPARepository<Customer,Long>

Create a new interface CustomCustomerRepository with a custom method signature.

public interface CustomCustomerRepository {
    public void customMethod();
}

Extend CustomerRepository interface using CustomCustomerRepository

public interface CustomerRepository extends JpaRepository<Customer, Long>, CustomCustomerRepository{

}

Create an implementation class named CustomerRepositoryImpl which implements CustomerRepository. Here you can inject the EntityManager using the @PersistentContext. Naming conventions matter here.

public class CustomCustomerRepositoryImpl implements CustomCustomerRepository {

    @PersistenceContext
    private EntityManager em;

    @Override
    public void customMethod() {
    
    }
}

Answer 2

In case you have many repositories to deal with, and your need in EntityManager is not specific for any particular repository, it is possible to implement various EntityManager functionality in a single helper class, maybe something like that:

@Service
public class RepositoryHelper {

    @PersistenceContext
    private EntityManager em;

    @Transactional
    public <E, R> R refreshAndUse(
            E entity,
            Function<E, R> usageFunction) {
        em.refresh(entity);
        return usageFunction.apply(entity);
    }

}

The refreshAndUse method here is a sample method to consume a detached entity instance, perform a refresh for it and return a result of a custom function to be applied to the refreshed entity in a declarative transaction context. And you can add other methods too, including query ones...