Hibernate延時加載:屬性延時加載與關係延時加載

Hibernate延遲加載:

1.屬性的延時加載

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();

		// 屬性延遲加載
		Employee employee = (Employee) session.load(Employee.class, 7);
		System.out.println("本行日誌之後纔開始執行sql語句(訪問數據庫),因爲下一條getName()語句將訪問屬性");
		System.out.println(employee.getName());

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

2.關係的延時加載

未開啓延時加載: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 提供對象與表的映射關係 -->
<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();
		
		/*// 屬性延遲加載
		Employee employee=(Employee)session.load(Employee.class, 7);
		System.out.println("本行日誌之後纔開始執行sql語句(訪問數據庫),因爲下一條getName()語句將訪問屬性");
		System.out.println(employee.getName());*/
		
		// 關係延遲加載
		Position position=(Position) session.get(Position.class, 3);
		
		System.out.println("程序將在本行日誌之前訪問數據庫");
		System.out.println(position.getEmployees());
		
		session.getTransaction().commit();
		session.close();
		sessionFactory.close();
	}
}

開啓延時加載: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();
		
		/*// 屬性延遲加載
		Employee employee=(Employee)session.load(Employee.class, 7);
		System.out.println("本行日誌之後纔開始執行sql語句(訪問數據庫),因爲下一條getName()語句將訪問屬性");
		System.out.println(employee.getName());*/
		
		// 關係延遲加載
		Position position=(Position) session.get(Position.class, 3);
		
		System.out.println("程序將在本行日誌會後訪問employee表,因爲開啓了延時加載並且getEmployee()在下一行");
		System.out.println(position.getEmployees());
		
		session.getTransaction().commit();
		session.close();
		sessionFactory.close();
	}
}

完~