为什么hibernate OneToMany @BatchSize不能工作？

Question

我正在使用Spring4.1.4.RELEASE+ hibernate 4.3.6.Final，我正在尝试@BatchSize用于OneToMany，但它似乎不起作用，下面是代码：

create table product (
    id int(6) unsigned auto_increment primary key,
    name varchar(30)
);

create table picture (
    id int(6) unsigned auto_increment primary key,
    product_id varchar(30),
    url varchar(30)
);

@Entity(name = "product")
public class Product extends BaseEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private int id;

    @Column(name = "name")
    private String name;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "product")
    @BatchSize(size=2)
    private List<Picture> pictures;

    public List<Picture> getPictures() {
        return pictures;
    }

    public void setPictures(List<Picture> pictures) {
        this.pictures = pictures;
    }
}


@Entity(name = "picture")
@BatchSize(size=10)
public class Picture extends BaseEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private int id;

    @Column(name = "url")
    private String url;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "product_id", referencedColumnName = "id")
    private Product product;

    public Product getProduct() {
        return product;
    }

    public void setProduct(Product product) {
        this.product = product;
    }
}


@Repository
public class ProductDao extends AbstractHibernateDao<Product> implements IProductDao {

    public ProductDao() {
        super();
        setClazz(Product.class);
    }

    @Override
    public Product find(final int id) {
        Product product = (Product) getCurrentSession().get(clazz, id);
System.out.println("*--------------------find-------------------------");
System.out.println(product.getPictures());
System.out.println("*--------------------end-------------------------");

        return product;
    }
}

我试图通过id查找Product，但是产品中没有任何图片，我也试图将BatchSize放在getPictures之上，但仍然无法工作。

我想知道我是不是错过了一些配置什么的，有人能帮忙吗？

更新：

这是日志：

[DEBUG] 2016-10-03 17:20:57.074 RequestMappingHandlerMapping:getHandlerInternal[302]: Returning handler method [public com.lehoolive.analyse.model.IResponse com.lehoolive.analyse.controller.ProductController.detail(int)]
[DEBUG] 2016-10-03 17:20:57.075 DispatcherServlet:doDispatch[931]: Last-Modified value for [/product/detail/1] is: -1
Hibernate: select product0_.id as id2_0_, product0_.name as name2_0_ from product product0_ where product0_.id=?
*--------------------find-------------------------
Hibernate: select pictures0_.product_id as product3_2_1_, pictures0_.id as id1_, pictures0_.id as id1_0_, pictures0_.product_id as product3_1_0_, pictures0_.url as url1_0_ from picture pictures0_ where pictures0_.product_id=?
[com.lehoolive.analyse.entity.Picture@29a0ce34, com.lehoolive.analyse.entity.Picture@5a7a10d8, com.lehoolive.analyse.entity.Picture@3e80350]
*--------------------end-------------------------
[DEBUG] 2016-10-03 17:20:57.333 ResponseBodyAdviceChain:invoke[61]: Invoking ResponseBodyAdvice chain for body=com.lehoolive.analyse.model.Response@59141f65

Answer 1

(摘自评论)

默认情况下，JPA无法告诉getPictures()返回数量有限的图片(afaik)。通常，我认为您不能限制返回的联接对象的数量。

如果要限制find方法返回的图片的数量，就必须编写自己的方法(@BatchSize只限制所做的SELECTS语句的数量，而不是结果的数量)。

您可以使用JPA:在图片上创建一个JPQL查询(而不是产品)，然后在.setMaxResult(2)之前添加.getResults() (您可以使用youPicturesList().get(0).getProduct();获得产品)

也许你可以用CriteriaBuilder来做你想做的事情，这可能允许你限制加入的数量，但是我从来没有这样使用过它。