Understanding how spring-data handles @EntityGraph

Question

(I made a SSCCE for this question.)

I have 2 simple entities : Employee and Company. Employee has a @ManyToOne relationship with Company with default fetch strategy (eager).

I want to be able to load the Employee without the Companywithout changing the fetch strategy defined in the Employee because I need to do that for only one use case.

JPA's entity graph seems to be intended for this purpose.

So I defined a @NamedEntityGraphon the class Employee:

@Entity
@NamedEntityGraph(name = "employeeOnly")
public class Employee {

  @Id
  private Integer id;
  private String name;
  private String surname;
  @ManyToOne
  private Company company;

  //Getters & Setters

And a EmployeeRepository like this :

public interface EmployeeRepository extends CrudRepository<Employee, Integer> {

  @EntityGraph(value = "employeeOnly", type = EntityGraph.EntityGraphType.FETCH)
  List<Employee> findByCompanyId(Integer companyId);

}

Despite the use of @EntityGraph, I can see in the logs that the Company is still loaded by hibernate :

2016-11-07 23:16:08.738 DEBUG 1029 --- [nio-8080-exec-2] org.hibernate.SQL                        : select employee0_.id as id1_1_, employee0_.company_id as company_4_1_, employee0_.name as name2_1_, employee0_.surname as surname3_1_ from employee employee0_ left outer join company company1_ on employee0_.company_id=company1_.id where company1_.id=?
2016-11-07 23:16:08.744 DEBUG 1029 --- [nio-8080-exec-2] org.hibernate.SQL                        : select company0_.id as id1_0_0_, company0_.name as name2_0_0_ from company company0_ where company0_.id=?

Why? How to avoid that?

Answer 1

Currently, Hibernate does not support handling non-lazy attributes as lazy, even with entity graphs. There is an open issue for this: HHH-8776.

So, the only solution for the time being is to make the association lazy.

Answer 2

Modified Answer

per-specification, the fetch type for @ManyToOne is EAGER by default. But even through we set:

@ManyToOne(fetch = FetchType.LAZY)
private Company company;

You will get the same result. The problem because the way spring-data-jpa create HQL/JPQL for you. So adding @ManyToOne(fetch = FetchType.LAZY) won't work is not enough. To solve this, use@ManyToOne(fetch = FetchType.LAZY) and @Query annotation in your repository:

Employee.java :

@ManyToOne(fetch = FetchType.LAZY)
private Company company;

EmployeeRepository.java

@Query("from Employee e where e.company.id = :companyId")
List<Employee> findByCompanyIdUsingQuery(@Param("companyId") Integer companyId);

In the test, this is SQL that generated by your loadByCompanyId() (which is generate left outer join):

select employee0_.id as id1_1_, employee0_.company_id as company_4_1_, employee0_.name as name2_1_, employee0_.surname as surname3_1_ from employee employee0_ left outer join company company1_ on employee0_.company_id=company1_.id where company1_.id=?

And this is SQL generated by method that use @Query annotation:

select employee0_.id as id1_1_, employee0_.company_id as company_4_1_, employee0_.name as name2_1_, employee0_.surname as surname3_1_ from employee employee0_ where employee0_.company_id=?

You could check the latest code in my repository.

HTH.