Hibernate 多对多与急切加载问题

Question

我对类的定义是这样的：

@Entity
@Table(name = "items")
public class Item {
    @Id
    @GeneratedValue
    private long id;

    @Column(unique = true, nullable = false)
    private String url;

    @ManyToMany(fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    private Collection<Tag> tags;

    @Column(columnDefinition = "TEXT")
    private String text;
}

当

 itemSession.createQuery("from Item i where i.url=?").setString(0, url)

需要使用两个 SQL 查询进行获取时：

select item0_.id as id1_,
       item0_.text as text1_, 
       item0_.url as url1_ 
   from items item0_ 
   where item0_.url=?

select tags0_.items_id as items1_1_1_, 
       tags0_.tags_id as tags2_1_,
       tag1_.id as id0_0_, tag1_.lastCrawlTime as lastCraw2_0_0_, 
       tag1_.name as name0_0_ 
  from items_tags tags0_ inner join tags tag1_ on tags0_.tags_id=tag1_.id 
  where tags0_.items_id=?

如何将其变成一个？

Answer 1

HQL 忽略映射中指定的获取策略。您应该使用强制加入

"from Item i join fetch i.tags where i.url=?"