传智播客Hibernate视频教程学习笔记15

多对一关系的检索：

在做查询的时候，Hibernate也会自动的填充Employee中的Department类型属性，部分测试代码如下：

test.java

import java.util.Date;
import java.util.List;

import org.hibernate.Criteria;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.criterion.Restrictions;

import domain.Department;
import domain.Employee;
import domain.Users;
import hibernate.HibernateUtil;

public class test {

/**
* @param args
*/
public static void main(String[] args) {
Department dpt = new Department();
dpt.setName("department_name");
Employee epy = new Employee();
epy.setName("employee_name");
epy.setDpt(dpt);

HibernateUtil.add(dpt);
HibernateUtil.add(epy);

epy = (Employee)HibernateUtil.get(Employee.class, 1);
System.out.println(epy.getName());
System.out.println(epy.getDpt().getName());

}
}

教程把打印的语句写在了事务里，所以懒加载是可以的，我没有放在一个事务里，所以懒加载的时候报错，no session。

我修改了映射文件，关闭了懒加载。正常运行。关于懒加载以后教程讲了再研究吧。

Employee.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="domain">
<class name="Employee">
<id name="id">
<generator class="native"/>
</id>
<property name="name"></property>
<many-to-one name="dpt" column="dpt_id" lazy="false"></many-to-one>//添加禁用懒加载
</class>
</hibernate-mapping>

这样测试起来就对了，Hibernate的sql语句为：

Hibernate: insert into Department (name) values (?)

Hibernate: insert into Employee (name, dpt_id) values (?, ?)

Hibernate: select employee0_.id as id2_0_, employee0_.name as name2_0_, employee0_.dpt_id as dpt3_2_0_ from Employee employee0_ where employee0_.id=?

Hibernate: select department0_.id as id1_0_, department0_.name as name1_0_ from Department department0_ where department0_.id=?

两条insert两条select，发现其实也无非封装了一下jdbc嘛。