JPA：选择实体的子集不会加载@OneToOne属性

Question

@Entity
public class GiganticEntity {

    @Id Long id;

    @OneToOne(mappedBy = "giganticEntity")
    Foo foo;

    @OneToOne(mappedBy = "giganticEntity")
    Bar bar;

    @OneToOne(mappedBy = "giganticEntity")
    Baz baz;

    // default constructor + getters/setters

    public GiganticEntity(Long id, Baz baz) {
        this.id = id;
        this.baz = baz;
    }
}

"SELECT new package.GiganticEntity(ge.id, ge.baz) " +
"FROM GiganticEntity ge WHERE ge.id = 1";

"SELECT new package.GiganticEntity(ge.id, b) FROM GiganticEntity ge " +
    "LEFT JOIN ge.baz as b " +
    "WHERE ge.id = 1";

"SELECT GiganticEntity g WHERE g.id = 1";

这在JPA中是可以实现的吗？我正在使用Hibernate作为它的实现。

编辑：查询实际上需要left join，所以我需要所有具有baz-es的大型实体。

Answer 1

因为GiganticEntity与BAZ有一对一的反向关联：

@OneToOne(mappedBy = "giganticEntity")
Baz baz;

这意味着Baz还与GiganticEntity有关联：

@OneToOne
GiganticEntity giganticEntity;

因此查询可以变为：

select new package.GiganticEntity(g.id, b)  
from Baz b
join b.giganticEntity g
where g.id : id

@Entity
@Table(name="GiganticEntity")
@Immutable
public class GignaticBazViewEntity {

    @Id Long id;

    @OneToOne(mappedBy = "bar")
    Bar bar;

    @OneToOne(mappedBy = "baz")
    Baz baz;

    public GiganticEntity(Long id, Bar bar, Baz baz) {
        this.id = id;
        this.bar = bar;
        this.baz = baz;
    }
}

select g
from GignaticBazViewEntity g
left join fetch g.bar
left join fetch g.baz
where g.id : id

select g
from GignaticBazViewEntity g
FETCH ALL PROPERTIES
where g.id : id