传智播客Hibernate视频教程学习笔记19

 test.java

import java.util.Date; import domain.IdCard; import domain.Person; import hibernate.HibernateUtil; public class test { /** * @param args */ public static void main(String[] args) { IdCard idCard = new IdCard(); idCard.setUsefulLife(new Date()); Person p = new Person(); p.setName("pf"); p.setIdCard(idCard); idCard.setPerson(p); HibernateUtil.add(p); HibernateUtil.add(idCard); p = (Person)HibernateUtil.get(Person.class, 1); System.out.println(p.getName()); System.out.println(p.getIdCard().getUsefulLife()); idCard = (IdCard)HibernateUtil.get(IdCard.class, 1); System.out.println(idCard.getUsefulLife()); System.out.println(idCard.getPerson().getName()); } }

查询的时候还是禁用了懒加载，否则在事务上还是会有一些问题，视频教程上对懒加载做了一定的说明。

在查主对象person的时候，Hibernate的sql语句

Hibernate: select person0_.id as id3_1_, person0_.name as name3_1_, idcard1_.id as id4_0_, idcard1_.userful_life as userful2_4_0_ from Person person0_ left outer join id_card idcard1_ on person0_.id=idcard1_.id where person0_.id=?

只有一条，是做了连接查询。

 

而在查询从对象idCard的时候，Hibernate的sql语句

Hibernate: select idcard0_.id as id4_0_, idcard0_.userful_life as userful2_4_0_ from id_card idcard0_ where idcard0_.id=?

Hibernate: select person0_.id as id3_1_, person0_.name as name3_1_, idcard1_.id as id4_0_, idcard1_.userful_life as userful2_4_0_ from Person person0_ left outer join id_card idcard1_ on person0_.id=idcard1_.id where person0_.id=?

做了两条查询

因为有懒加载机制的存在，现在也不是很明白。