Hibernate - Projections and fetching strategy of entity

Question

So here is my problem:

I have 2 classes Person and department.

Person :

@Entity
public class Personne
{
    @Id
    private Long id;

    private String name;

    @ManyToOne(fetch=FetchType.EAGER)
    @JoinColumn(name="dept_id")
    @Fetch(FetchMode.JOIN)
    private Departement dept;


    // getter & setter
}

Department :

@Entity
public class Departement
{
    @Id
    private Long id;

    private String name;

    // getter & setter

}

I want to select only departement of a personn with a criteria query so i use Projection:

My Code :

Criteria crt = session.createCriteria(Personne.class);
            crt.createAlias("dept", "d",JoinType.LEFT_OUTER_JOIN);
            crt.setProjection(Projections.projectionList().add(Projections.property("dept")));
            crt.add(Restrictions.eq("id", 1L));

Above query works well but i get 2 queries whereas i expect only 1 since my fetch type is eager.

Log :

[use] 2017-08-16 16:23:07,113 DEBUG [main] SqlStatementLogger.logStatement(109) | select this_.dept_id as y0_ from Personne this_ left outer join Departement d1_ on this_.dept_id=d1_.id where this_.id=?
[use] 2017-08-16 16:23:07,119 DEBUG [main] SqlStatementLogger.logStatement(109) | select departemen0_.id as id1_0_0_, departemen0_.name as name2_0_0_ from Departement departemen0_ where departemen0_.id=?

it seems that projection of entity fires n+1 select. Does that make sense?

can anyone help me with this?

Thanks

Answer 1

EAGER does not mean that less queries will be performed, only that the queries will be performed when the owner entity is queried.

What you can use is the @FetchMode annotation, in your case I would assume you would want a FetchMode.JOIN.

FechtMode javadoc: https://docs.jboss.org/hibernate/orm/5.2/javadocs/org/hibernate/FetchMode.html

Either way, be careful with the results, please check the gabrielgiussi answer from FetchMode Join vs SubSelect as he goes into detail how the fetch modes work.