JPA @OneToOne 选择带有 N+1 个查询的列表

Question

我实际上是在尝试使用 JPA@OneToOne注释将Child实体链接到它的Parent.

它运行良好，除了在获取Childs列表时，JPA 引擎（在本例中为 Hibernate）进行 1+n 次查询。

这是 Hibernate 查询的日志：

select child0_.id as id1_0_, child0_.parent as parent3_0_, child0_.value as value2_0_ from child child0_
select parent0_.id as id1_1_0_, parent0_.something as somethin2_1_0_ from parent parent0_ where parent0_.id=?
select parent0_.id as id1_1_0_, parent0_.something as somethin2_1_0_ from parent parent0_ where parent0_.id=?
select parent0_.id as id1_1_0_, parent0_.something as somethin2_1_0_ from parent parent0_ where parent0_.id=?

使用完全相同的实体定义，特别是当我得到一个孩子时，JPA 使用预期的 JOIN 执行查询：

select child0_.id as id1_0_0_, child0_.parent as parent3_0_0_, child0_.value as value2_0_0_, parent1_.id as id1_1_1_, parent1_.something as somethin2_1_1_ from child child0_ left outer join parent parent1_ on child0_.parent=parent1_.id where child0_.id=?

这是Child实体定义：

@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
@Entity
@Table(name = "child")
public class Child {

    @Id
    private Long   id;
    @Column
    private String value;
    @OneToOne(optional = false)
    @JoinColumn(name = "parent")
    private Parent parent;

}

和Parent实体：

@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
@Entity
@Table(name = "parent")
public class Parent {

    @Id
    private Long   id;
    @Column
    private String something;

}

您可以在此处找到运行代码的完整示例：https : //github.com/Alexandre-Carbenay/demo-jpa-onetoone

有没有办法在获取Child实体列表时避免 1+n 查询Parent？

Answer 1

我终于找到了一个比JOIN FETCHQueryDsl 更好的解决方案，@EntityGraph在存储库方法上使用注释。

这是更新的Child定义：

@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
@Entity
@NamedEntityGraph(name = "Child.withParent", attributeNodes = @NamedAttributeNode("parent"))
@Table(name = "child")
public class Child {
    @Id
    private Long   id;
    @Column
    private String value;
    @OneToOne(optional = false)
    @JoinColumn(name = "parent")
    private Parent parent;
}

和ChildJpaRepository定义：

public interface ChildJpaRepository extends JpaRepository<Child, Long>, QueryDslPredicateExecutor<Child> {

    @Override
    @EntityGraph("Child.withParent")
    List<Child> findAll();

    @Override
    @EntityGraph("Child.withParent")
    List<Child> findAll(Predicate predicate);

}

感谢 Simon Martinelli 和 Vlad Mihalcea 的帮助