@BatchSize，但在获取@ManyToOne关联时有许多往返

Question

我将分页与hibernate的spring-data-jpa和querydsl一起使用@BatchSize(size=10)，并且我只用于一次往返数据库。

@Entity
@Table(name = "appel_offre", catalog = "ao")
public class AppelOffre implements java.io.Serializable {

    ....
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "appelOffre")
    @BatchSize(size=10)
    public Set<AoActivite> getAoActivites() {
        return this.aoActivites;
    }

和：

@Entity
@Table(name = "ao_activite", catalog = "ao")
public class AoActivite implements java.io.Serializable {
    .....
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ID_ACTIVITE", nullable = false)
    @BatchSize(size=10)
    public Activite getActivite() {
        return this.activite;
    }

我的查询

JPAQuery query = new JPAQuery(entityManager).from(ao)

    .leftJoin( ao.acheteur, ach ).fetch()

    .leftJoin( ao.aoActivites , ao_ac )
    .leftJoin( ao_ac.activite , ac )
    .offset(...).limit(...).list(..);

但是在日志中有很多往返数据库的行程：

1 - round-trip

.....
Hibernate: select ... from ao.ao_activite aoactivite0_ where aoactivite0_.ID_APPEL_OFFRE in (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?

2 - round-trip

.....
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?

3 - round-trip

.....
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?

4 - round-trip

.....
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?

5 - round-trip

.....

6 - round-trip

.....
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?

7 - round-trip

......

8 - round-trip

.....
Hibernate: select ... from ao.activite activite0_ where activite0_.ID_ACTIVITE=?

9 - round-trip

.....

10 - round-trip

Answer 1

该@BatchSize两个有道理

• One-To-Many 和
• Many-to-One 以及

以防万一Many-To-One，我们必须在@Entity级别上应用它（在我们的Activite类映射中）

@Entity
@BatchSize(size=25)
@Table(name = "activite" ...
public class Activite implements java.io.Serializable {
...

在doc中检查它 （ 在 下面附加小引用） ：

[20.1.5。使用批量提取](http://docs.jboss.org/hibernate/orm/4.3/manual/en-

US/html_single/#performance-fetching-batch)

…

批量获取类/实体更容易理解。考虑以下示例：在运行时，您在一个Session中加载了25个Cat实例，并且每个实例Cat都引用了其所有者Person。在Person类的映射使用了代理服务器，为lazy
=“真”。如果您现在遍历所有的猫并调用getOwner()它们，默认情况下，Hibernate将执行25条SELECT语句以检索代理的所有者。您可以通过在Person映射中指定一个批处理大小来调整此行为：

<class name="Person" batch-size="10">...</class>

…