Question

我正在使用spring 4.1.4.RELEASE + hibernate 4.3.6.Final，我正在为OneToMany尝试@BatchSize，但它似乎不起作用，这里是代码：

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找到Product，但是产品里面没有任何图片，我也尝试将BatchSize放在getPictures之上，但它仍然不起作用。

我想知道我是否错过了某些配置或什么，有人可以帮忙吗？

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

（来自评论）

默认情况下，没有办法告诉JPA getPictures（）返回有限数量的图片（afaik）。一般来说，我认为你不能限制返回的联接对象的数量。

如果要限制find方法返回的图片数量，则必须编写自己的方法（@BatchSize仅限制SELECTS语句的数量，而不是结果数量）。

您可以使用JPA执行此操作：在图片（而非产品）上创建JPQL查询，然后在.setMaxResult(2)之前添加.getResults()（并且您可以使用youPicturesList().get(0).getProduct();获取产品）

也许你可以用CriteriaBuilder做你想做的事情，这可能会让你限制加入的参与者，但我从来没有像这样使用它。

为什么hibernate OneToMany @BatchSize不起作用？

1 个答案: