为什么hibernate执行两个查询以急切加载@OneToOne双向关联？
我有实体A有一个B实体，而B有一个带有@OneToOne双向关联的A.
现在，当我找到所有A记录时，hibernate在B上执行左外连接的两个查询，如下所示：
select a.id, a.id_b, a.field1, b.id, b.field1 from A as a, B as b left outer join b ON b.id=a.id_b;
select a.id, a.id_b, a.field1, b.id, b.field1 from A as a, B as b left outer join b ON b.id=a.id_b WHERE b.id=?
@Entity
public class A implements Serializable{
// id and other ecc ecc
@OneToOne
@JoinColumn(name="id_b")
B b;
}
@Entity
public class B implements Serializable{
// id and other ecc ecc
@OneToOne(mappedBy="b")
A a;
}
没有找到相关结果
已邀请:
2 个回复
外镶受继
@Entity public class A implements Serializable { private MutableInt id = new MutableInt(); private B b; public void setIdAsMutableInt(MutableInt id) { this.id = id; } @Id @GeneratedValue public Integer getId() { return id.intValue(); } public void setId(Integer id) { this.id.setValue(id); } /** * Any ToOne annotation, such as @OneToOne and @ManyToOne, is EARGELY loaded, by default */ @OneToOne(fetch=FetchType.LAZY) @PrimaryKeyJoinColumn @Cascade(CascadeType.SAVE_UPDATE) public B getB() { return b; } public void setB(B b) { b.setIdAsMutableInt(id); this.b = b; } }@Entity public class B implements Serializable { private MutableInt id = new MutableInt(); private A a; public void setIdAsMutableInt(MutableInt id) { this.id = id; } @Id public Integer getId() { return id.intValue(); } public void setId(Integer id) { this.id.setValue(id); } @OneToOne(fetch=FetchType.LAZY) @PrimaryKeyJoinColumn public A getA() { return a; } public void setA(A a) { this.a = a; } }A a = new A(); B b = new B(); a.setB(b); /** * b property will be saved because Cascade.SAVE_UPDATE */ Serializable id = session.save(a); b = (B) session .createQuery("from B b left join fetch b.a where b.id = :id") .setParameter("id", id) .list() .get(0); Assert.assertEquals(b.getId(), b.getA().getId());@Entity public class A implements Serializable { private Integer id; private B b; @Id @GeneratedValue public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } /** * mappedBy="a" means: Look at "a" field / property at B Entity. If it has any assigned value, join us Through B_ID foreign key column */ @OneToOne(fetch=FetchType.LAZY, mappedBy="a") /** * Table A has a foreign key column called "B_ID" */ @JoinColumn(name="B_ID") @Cascade(CascadeType.SAVE_UPDATE) public B getB() { return b; } public void setB(B b) { this.b = b; } }@Entity public class B implements Serializable { private Integer id; private A a; public void setIdAsMutableInt(MutableInt id) { this.id = id; } @Id @GeneratedValue public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } @OneToOne(fetch=FetchType.LAZY) public A getA() { return a; } public void setA(A a) { this.a = a; } }A a = new A(); B b = new B(); /** * Set up both sides * Or use some kind of add convenience method */ a.setB(b); b.setA(a); /** * b property will be saved because Cascade.SAVE_UPDATE */ Serializable id = session.save(a); b = (B) session .createQuery("from B b left join fetch b.a where b.id = :id") .setParameter("id", id) .list() .get(0);亲奋漏
和类是否正确实现了和，这样Hibernate可以告诉指向的实例与第一个的实例相同？ 听起来您正在尝试建模双向一对一映射 - 请查看本手册中的部分，以查看完成它的推荐方法。