保存后刷新并获取实体（JPA/Spring Data/Hibernate）

Instead of defining EntityManager in each of your resource, you can define it once by creating a Custom JpaRepository. Reference

Then use the refresh of your EntityManager in each of your repository directly.

Refer the below example:

CustomRepository Interface

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.NoRepositoryBean;

import java.io.Serializable;

@NoRepositoryBean
public interface CustomRepository<T, ID extends Serializable> extends JpaRepository<T, ID> {
  void refresh(T t);
}

CustomRepository Implementation

import org.springframework.data.jpa.repository.support.JpaEntityInformation;
import org.springframework.data.jpa.repository.support.SimpleJpaRepository;
import org.springframework.transaction.annotation.Transactional;

import javax.persistence.EntityManager;
import java.io.Serializable;

public class CustomRepositoryImpl<T, ID extends Serializable> extends SimpleJpaRepository<T, ID>
    implements CustomRepository<T, ID> {

  private final EntityManager entityManager;

  public CustomRepositoryImpl(JpaEntityInformation entityInformation, EntityManager entityManager) {
    super(entityInformation, entityManager);
    this.entityManager = entityManager;
  }

  @Override
  @Transactional
  public void refresh(T t) {
    entityManager.refresh(t);
  }
}

Enable Custom JPARepository in Spring Boot Application Class

@SpringBootApplication
@EnableJpaRepositories (repositoryBaseClass = CustomRepositoryImpl.class)
public class Application {
  public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
  }
}

Your Something Repository

public interface SomethingRepository extends CustomRepository<Something, Long> {

}

Use Refresh directly in SomethingResource (Assuming Something is an Entity)

@RestController
@RequestMapping("/api")
@Transactional
public class SomethingResource {

    private final SomethingRepository somethingRepository;

    public SomethingResource(SomethingRepository somethingRepository) {
        this.somethingRepository = somethingRepository;
    }

    @PostMapping("/somethings")
    public Something createSomething(@RequestBody Something something) throws URISyntaxException {
        Something result = somethingRepository.save(something);
        somethingRepository.refresh(result);
        return result;
    }
}

That's not enough:

Something result = somethingRepository.save(something);

You need to manually merge the incoming entity:

Something dbSomething = somethingRepository.findOne(
    Something.class, something.getId()
);
dbSomething.setName(something.getName());
dbSomething.setOwner(something.getOwner());

somethingRepository.save(dbSomething);

Since the property attribute is using the default FetchType.EAGER, the entity should have the property attribute initialized.

But, that's strange to call the Repository twice from the REST controller. You should have a Service layer that does all that in a @Transactional service method. That way, you don't need to resave the entity since it's already managed.

@Transactional
public Something mergeSomething(Something something) {
    Something dbSomething = somethingRepository.findOne(
        Something.class, something.getId()
    );
    dbSomething.setName(something.getName());
    dbSomething.setOwner(something.getOwner());

    return dbSomething;
}

Now, you need to carefully merge every property you sent. In your case, if you send null for property you should decide whether you should nullify the @ManyToOne reference or not. So, it depends on your current application business logic requirements.

Update

If you make sure you always send back the same entity you previously fetched, you could just use merge.

em.merge(result);

But your property attribute is just an id, and not an actual child entity, so you have to resolve that yourself in the Service layer.

In Spring Boot JpaRepository:

If our modifying query changes entities contained in the persistence context, then this context becomes outdated.

In order to fetch the entities from the database with latest record.

Use @Modifying(clearAutomatically = true)

@Modifying annotation has clearAutomatically attribute which defines whether it should clear the underlying persistence context after executing the modifying query.

Example:

@Modifying(clearAutomatically = true)
@Query("UPDATE NetworkEntity n SET n.network_status = :network_status WHERE n.network_id = :network_id")
        int expireNetwork(@Param("network_id") Integer network_id,  @Param("network_status") String network_status);

By the time you persist the entity it will be in managed state so if you just call something.getProperty(); it loads from the database and fills the property value of the something entity

public Something save(Something something) {
    em.persist(something);
    something.getProperty();
    return something;
}

so normally when you have many-to-one relationship that should be fetched automatically. If not calling the getters of the objects in entity will fill them too by firing a new DB Find request.