Posted on 2007-12-10 12:52
G_G 阅读(1285)
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hibernate
表关系 T1oo ->ont-to-many-> T2oo (t1oo.id-t2oo.aid)
1.单条select延迟加载
Iterator it = session.createQuery("from T1oo ").iterate();
while(it.hasNext()){
T1oo t1 = (T1oo)it.next();
t1.getName();
}
/*运行语句 n+1
这就只加载 id
Hibernate: select t1oo0_.id as col_0_0_ from t1oo t1oo0_
此是在 t1.getName(); 延迟加载的
Hibernate: select t1oo0_.id as id0_, t1oo0_.name as name0_0_ from t1oo t1oo0_ where t1oo0_.id=?
Hibernate: select t1oo0_.id as id0_, t1oo0_.name as name0_0_ from t1oo t1oo0_ where t1oo0_.id=?
*/
2.级连查询：
1)set排序 <set ... order-by="avg desc" ...> 从大到小
2）batch-size="10" 用法是
select * from t2oo where aid in (?,?,?....)
3)
如果想忽略延迟，并有一定逻辑全部加载，这有两中解决办法：
1).内连
mysql> select *
-> from t1oo t1oo0_ inner join t2oo t2ooset1_ on t1oo0_.id=t2ooset1_.aid;
+----+-----------+----+-----+------+---------+
| id | name | id | avg | aid | version |
+----+-----------+----+-----+------+---------+
| 1 | liukaiyi | 1 | 23 | 1 | 1 |
| 1 | liukaiyi | 2 | 24 | 1 | 1 |
| 1 | liukaiyi | 3 | 25 | 1 | 1 |
| 2 | liukaiyi2 | 4 | 26 | 2 | 0 |
+----+-----------+----+-----+------+---------+
Iterator it = new HashSet(session.createQuery("from T1oo t1 inner join fetch t1.t2ooSet t2where t2.id<=3").list()).iterator();
while(it.hasNext()){
T1oo t1 = (T1oo)it.next();
System.out.println(t1.getName());
for(Iterator itr=t1.getT2ooSet().iterator();itr.hasNext(); ){
T2oo t2 = (T2oo)itr.next();
System.out.println(" "+ t2.getAvg() );
}
}
结果是：
Hibernate: select t1oo0_.id as id0_, t2ooset1_.id as id1_, t1oo0_.name as name0_0_, t2ooset1_.version as version1_1_, t2ooset1_.avg as avg1_1_, t2ooset1_.aid as aid1_1_, t2ooset1_.aid as aid0__, t2ooset1_.id as id0__ from t1oo t1oo0_ inner join t2oo t2ooset1_ on t1oo0_.id=t2ooset1_.aid where t2ooset1_.id<=3
liukaiyi
24
23
25