HIbernate fetch join issuing additional sql statements.

Question

Consider the following Parent class that has two ManyToOne references.

@Entity
@Table(name = "PARENT")
public class Parent {

private static final long serialVersionUID = 3730163805206219313L;

@Id
@SequenceGenerator(name = "SEQ#PARENT", sequenceName = "SEQ#PARENT", allocationSize = 1)
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ#PARENT")
@Column(name = "ID")
private long id;

@ManyToOne(optional = false, fetch=FetchType.EAGER)
@Fetch(FetchMode.JOIN)
@JoinColumn(name="CHILD_1_ID", referencedColumnName="FK_COLUMN_NAME")
private Child childInstance1;

@ManyToOne(optional = false, fetch=FetchType.EAGER)
@Fetch(FetchMode.JOIN)
@JoinColumn(name="CHILD_2_ID", referencedColumnName="FK_COLUMN_NAME")
private Child childInstance2;

@Column(name = "USER_ID")
private String userId;              
}

I am using the following hql query to load the Parent instance:

"from Parent p  join fetch p.childInstance1 join fetch p.childInstance2 where p.userId = :userId"

This always results in hibernate issuing separate sql statements to load the childInstance1 rows even though it does the fetch join.

Any help in avoiding the extra sql statements is appreciated.

Answer 1

I cannot reproduce. Given the following entities:

@Entity
public class Parent3764122 {
    @Id @GeneratedValue
    private long id;

    @ManyToOne(optional = false/*, fetch=FetchType.EAGER*/) // EAGER by default
    //@Fetch(FetchMode.JOIN) // unnecessary
    @JoinColumn(name="CHILD_1_ID")
    private Child3764122 childInstance1;

    @ManyToOne(optional = false/*, fetch=FetchType.EAGER*/) // EAGER by default
    //@Fetch(FetchMode.JOIN) // unnecessary
    @JoinColumn(name="CHILD_2_ID")
    private Child3764122 childInstance2;

    @Column(name = "USER_ID")
    private String userId;
    ...
}

and

@Entity
public class Child3764122 {
    @Id @GeneratedValue
    private Long id;

    ...
}

The following HQL query:

from Parent3764122 p join fetch p.childInstance1 join fetch p.childInstance2 where p.id = :id

Generates the following SQL:

select
    parent3764x0_.id as id129_0_,
    child37641x1_.id as id130_1_,
    child37641x2_.id as id130_2_,
    parent3764x0_.CHILD_1_ID as CHILD3_129_0_,
    parent3764x0_.CHILD_2_ID as CHILD4_129_0_,
    parent3764x0_.USER_ID as USER2_129_0_ 
from
    Parent3764122 parent3764x0_ 
inner join
    Child3764122 child37641x1_ 
        on parent3764x0_.CHILD_1_ID=child37641x1_.id 
inner join
    Child3764122 child37641x2_ 
        on parent3764x0_.CHILD_2_ID=child37641x2_.id 
where
    parent3764x0_.id=?

Works as expected with Hibernate 3.3.0.SP1, Hibernate Annotations 3.4.0.GA.