最近在做一个Flex项目,后台spring+hibernate+blazeDS,由于blazeDS不支持延迟加载,逼得我非得把延迟加载关掉,由于我用的是注释配置,我就直接在EJB3的@ManyToMany注解里加了fetch=FetchType.EAGER,详细配置如下
User.java
@ManyToMany(cascade = { CascadeType.PERSIST, CascadeType.MERGE },fetch=FetchType.EAGER)
//多对多定义.
@JoinTable(name = "USERS_ROLES", joinColumns = { @JoinColumn(name = "USER_ID") }, inverseJoinColumns = { @JoinColumn(name = "ROLE_ID") })
//集合按id排序.
@OrderBy("id")
//集合中对象的id的缓存.
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public Set<Role> getRoles() {
return roles;
}
运行之后发现一个奇怪现象,查询出来的结果每个对象都重复了3份儿,到控制台看生成的SQL语句,发现是用的left outer join,
Hibernate:
select
this_.id as id2_2_,
this_.email as email2_2_,
this_.login_name as login3_2_2_,
this_.name as name2_2_,
this_.password as password2_2_,
roles2_.user_id as user1_4_,
role3_.id as role2_4_,
role3_.id as id1_0_,
role3_.name as name1_0_,
auths4_.role_id as role1_5_,
authority5_.id as authority2_5_,
authority5_.id as id0_1_,
authority5_.display_name as display2_0_1_,
authority5_.name as name0_1_
from
users this_
left outer join
users_roles roles2_
on this_.id=roles2_.user_id
left outer join
roles role3_
on roles2_.role_id=role3_.id
left outer join
roles_authorities auths4_
on role3_.id=auths4_.role_id
left outer join
authorities authority5_
on auths4_.authority_id=authority5_.id
order by
role3_.id asc,
authority5_.id asc
越看越不对,拷到mysql控制台执行结果还是重复~看来干脆就是SQL语句的问题,左外连接没有过滤结果集。查了查Hibernate手册,转而用
@Fetch(FetchMode.SUBSELECT)
@LazyCollection(LazyCollectionOption.FALSE)
代替原来的fetch=FetchType.EAGER,使用子查询加载集合,测试成功,看来Hibernate也有靠不住的时候,谁能告诉我怎么用left outer join得到正确的结果???毕竟用了子查询的话会多发几条SQL语句,还是看着不爽。