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。