Hibernate延时加载:属性延时加载与关系延时加载

Hibernate延迟加载:

1.属性的延时加载
package com.joey.test;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import com.joey.pojo.Employee;
import com.joey.pojo.Position;

public class Hibernate_lazyload {

public static void main(String[] args) {
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();

Session session = sessionFactory.openSession();
session.beginTransaction();

// 属性延迟加载
Employee employee = (Employee) session.load(Employee.class, 7);
System.out.println("本行日志之后才开始执行sql语句(访问数据库),因为下一条getName()语句将访问属性");
System.out.println(employee.getName());

session.getTransaction().commit();
session.close();
sessionFactory.close();
}
}




2.关系的延时加载

未开启延时加载:Position.xml

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

<!-- Posotion.hbm.xml 提供对象与表的映射关系 -->
<hibernate-mapping package="com.joey.pojo">
<class name="Position" table="position">
<id name="id" column="id">
<generator class="native">
</generator>
</id>
<property name="positionName" />

<set name="employees" lazy="false"><----------------lazy="false"()
<key column="cid" not-null="false"></key>
<one-to-many class="Employee" />
</set>
</class>
</hibernate-mapping>

package com.joey.test;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import com.joey.pojo.Employee;
import com.joey.pojo.Position;

public class Hibernate_lazyload {

public static void main(String[] args) {
SessionFactory sessionFactory=new Configuration().configure().buildSessionFactory();

Session session=sessionFactory.openSession();
session.beginTransaction();

/*// 属性延迟加载
Employee employee=(Employee)session.load(Employee.class, 7);
System.out.println("本行日志之后才开始执行sql语句(访问数据库),因为下一条getName()语句将访问属性");
System.out.println(employee.getName());*/

// 关系延迟加载
Position position=(Position) session.get(Position.class, 3);

System.out.println("程序将在本行日志之前访问数据库");
System.out.println(position.getEmployees());

session.getTransaction().commit();
session.close();
sessionFactory.close();
}
}

开启延时加载:Position.xml
<set name="employees" lazy="true">

package com.joey.test;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import com.joey.pojo.Employee;
import com.joey.pojo.Position;

public class Hibernate_lazyload {

public static void main(String[] args) {
SessionFactory sessionFactory=new Configuration().configure().buildSessionFactory();

Session session=sessionFactory.openSession();
session.beginTransaction();

/*// 属性延迟加载
Employee employee=(Employee)session.load(Employee.class, 7);
System.out.println("本行日志之后才开始执行sql语句(访问数据库),因为下一条getName()语句将访问属性");
System.out.println(employee.getName());*/

// 关系延迟加载
Position position=(Position) session.get(Position.class, 3);

System.out.println("程序将在本行日志会后访问employee表,因为开启了延时加载并且getEmployee()在下一行");
System.out.println(position.getEmployees());

session.getTransaction().commit();
session.close();
sessionFactory.close();
}
}