（五）Hibernate 操作对象

所有项目导入对应的hibernate的jar包、mysql的jar包和添加每次都需要用到的HibernateUtil.java

第一节：Hibernate 中四种对象状态

临时状态(transient)：刚用new 语句创建，还没有被持久化，并且不处于Sesssion 的缓存中。处于临时状态的Java 对象被称为临时对象。

持久化状态(persistent)：已经被持久化，并且加入到Session 的缓存中。处于持久化状态的Java 对象被称为持久化对象。

删除状态(removed)：不再处于Session 的缓存中，并且Session 已经计划将其从数据库中删除。处于删除状态的Java 对象被称为删除对象。

游离状态(detached)：已经被持久化，但不再处于Session 的缓存中。处于游离状态的Java 对象被称为游离对象。

例子：

hibernate.cfg.xml

 <?xml version='1.0' encoding='utf-8'?>
 <!DOCTYPE hibernate-configuration PUBLIC
         "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
         "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 
 <hibernate-configuration>
 
     <session-factory>
 
         <!--数据库连接设置 -->
         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
         <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
         <property name="connection.username">root</property>
         <property name="connection.password">123456</property>
 
         <!-- 方言 -->
         <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
 
         <!-- 控制台显示SQL -->
         <property name="show_sql">true</property>
 
         <!-- 自动更新表结构 -->
         <property name="hbm2ddl.auto">update</property>
 
           <mapping resource="com/wishwzp/model/Student.hbm.xml"/>
 
           <mapping resource="com/wishwzp/model/Class.hbm.xml"/>
 
     </session-factory>
 
 </hibernate-configuration>

Class.java

 package com.wishwzp.model;
 
 public class Class {
 
     private long id;
     private String name;
 
     public long getId() {
         return id;
     }
     public void setId(long id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
 
 }

Class.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC
         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 
 <hibernate-mapping package="com.wishwzp.model">
 
     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>
 
         <property name="name" column="className"></property>
     </class>
 
 </hibernate-mapping>

Student.java

 package com.wishwzp.model;
 
 public class Student {
 
     private long id;
     private String name;
     private Class c;
 
     public long getId() {
         return id;
     }
     public void setId(long id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
 
     public Class getC() {
         return c;
     }
     public void setC(Class c) {
         this.c = c;
     }
     @Override
     public String toString() {
         return "Student [id=" + id + ", name=" + name + "]";
     }
 
 }

Student.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC
         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 
 <hibernate-mapping package="com.wishwzp.model">
 
     <class name="Student" table="t_student">
         <id name="id" column="stuId">
             <generator class="native"></generator>
         </id>
 
         <property name="name" column="stuName"></property>
 
         <many-to-one name="c" column="classId" class="com.wishwzp.model.Class" cascade="save-update"></many-to-one>
     </class>
 
 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.service;
 
 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 
 import com.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;
 
 public class StudentTest {
 
     public static void main(String[] args) {
         SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
         Session session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
 
         Class c1=new Class(); // 临时对象1
         c1.setName("08计本");
 
         Class c2=new Class();  // 临时对象2
         c2.setName("09计本");
 
         session.save(c1); // 持久化对象
         session.save(c2); // 持久化对象
 
         session.delete(c2); // 删除对象
 
         session.getTransaction().commit(); // 提交事务
         session.close(); // 关闭session
 
         System.out.println(c1.getName()); // 游离对象
         System.out.println(c2.getName()); // 删除对象
     }
 }

结果显示：

第二节：Session 常用方法讲解

1，save()方法将一个临时对象转变成持久化对象；

2，load()方法VS get()方法

都是根据OID 从数据库中加载一个持久化对象。

区别1：假如数据库中不存在与OID 对应的记录，Load()方法会抛出异常，而get()方法返回null;

区别2：load 方法默认采用延迟加载策略，get 方法采用立即检索策略；

2，update()方法将一个游离对象转变为持久化对象；

3，saveOrUpdate()方法包含了save()和update()方法；

4，merge()方法，合并对象；

5，delete()方法，删除对象；

例子：

hibernate.cfg.xml

 <?xml version='1.0' encoding='utf-8'?>
 <!DOCTYPE hibernate-configuration PUBLIC
         "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
         "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 
 <hibernate-configuration>
 
     <session-factory>
 
         <!--数据库连接设置 -->
         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
         <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
         <property name="connection.username">root</property>
         <property name="connection.password">123456</property>
 
         <!-- 方言 -->
         <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
 
         <!-- 控制台显示SQL -->
         <property name="show_sql">true</property>
 
         <!-- 自动更新表结构 -->
         <property name="hbm2ddl.auto">update</property>
 
           <mapping resource="com/wishwzp/model/Student.hbm.xml"/>
 
           <mapping resource="com/wishwzp/model/Class.hbm.xml"/>
 
     </session-factory>
 
 </hibernate-configuration>

Class.java

 package com.wishwzp.model;
 
 import java.util.HashSet;
 import java.util.Set;
 
 public class Class {
 
     private long id;
     private String name;
     private Set<Student> students=new HashSet<Student>();
 
     public long getId() {
         return id;
     }
     public void setId(long id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public Set<Student> getStudents() {
         return students;
     }
     public void setStudents(Set<Student> students) {
         this.students = students;
     }
 
 }

Class.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC
         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 
 <hibernate-mapping package="com.wishwzp.model">
 
     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>
 
         <property name="name" column="className"></property>
 
         <set name="students" cascade="delete" inverse="true">
             <key column="classId"></key>
             <one-to-many class="com.wishwzp.model.Student"/>
         </set>
     </class>
 
 </hibernate-mapping>

Student.java

 package com.wishwzp.model;
 
 public class Student {
 
     private long id;
     private String name;
     private Class c;
 
     public long getId() {
         return id;
     }
     public void setId(long id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
 
     public Class getC() {
         return c;
     }
     public void setC(Class c) {
         this.c = c;
     }
     @Override
     public String toString() {
         return "Student [id=" + id + ", name=" + name + "]";
     }
 
 }

Studnet.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC
         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 
 <hibernate-mapping package="com.wishwzp.model">
 
     <class name="Student" table="t_student">
         <id name="id" column="stuId">
             <generator class="native"></generator>
         </id>
 
         <property name="name" column="stuName"></property>
 
         <many-to-one name="c" column="classId" class="com.wishwzp.model.Class" cascade="save-update"></many-to-one>
     </class>
 
 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.service;
 
 import java.util.Iterator;
 import java.util.Set;
 
 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 
 import com.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;
 
 public class StudentTest {
 
     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;
 
     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }
 
     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }
 
     //save()方法
     @Test
     public void testSaveClassAndStudent() {
         Class c=new Class();
         c.setName("08计本");
 
         Student s1=new Student();
         s1.setName("张三");
         s1.setC(c);
 
         Student s2=new Student();
         s2.setName("李四");
         s2.setC(c);
 
         session.save(s1);
         session.save(s2);
 
     }
 
     //load()方法和get()方法的区别
     //Load()方法会抛出异常，而get()方法返回null;
     @Test
     public void testLoadClass(){
         // Class c=(Class)session.load(Class.class, Long.valueOf(2));
         Class c=(Class)session.load(Class.class, Long.valueOf(1));
         System.out.println(c.getStudents());
     }
 
     @Test
     public void testGetClass(){
         // Class c=(Class)session.get(Class.class, Long.valueOf(2));
         Class c=(Class)session.get(Class.class, Long.valueOf(1));
         System.out.println(c.getStudents());
     }
 
     //update()方法
     @Test
     public void testUpdateClass(){
         Session session1=sessionFactory.openSession();
         session1.beginTransaction();
         Class c=(Class)session1.get(Class.class, Long.valueOf(1));
         session1.getTransaction().commit(); // 提交事务
         session1.close();
 
         Session session2=sessionFactory.openSession();
         session2.beginTransaction();
         c.setName("08计算机本科2");
         session2.update(c);
         session2.getTransaction().commit(); // 提交事务
         session2.close();
     }
 
     //saveOrUpdate()方法
     @Test
     public void testSaveOrUpdateClass(){
         Session session1=sessionFactory.openSession();
         session1.beginTransaction();
         Class c=(Class)session1.get(Class.class, Long.valueOf(1));
         session1.getTransaction().commit(); // 提交事务
         session1.close();
 
         Session session2=sessionFactory.openSession();
         session2.beginTransaction();
         c.setName("08计算机本科3");
 
         Class c2=new Class();
         c2.setName("09计算机本科3");
         session2.saveOrUpdate(c);
         session2.saveOrUpdate(c2);
         session2.getTransaction().commit(); // 提交事务
         session2.close();
     }
 
     //merge()方法
     @Test
     public void testMergeClass(){
         Session session1=sessionFactory.openSession();
         session1.beginTransaction();
         Class c=(Class)session1.get(Class.class, Long.valueOf(1));
         session1.getTransaction().commit(); // 提交事务
         session1.close();
 
         Session session2=sessionFactory.openSession();
         session2.beginTransaction();
 
         Class c2=(Class)session2.get(Class.class, Long.valueOf(1));
         c.setName("08计算机本科4");
 
         session2.merge(c);
 
         session2.getTransaction().commit(); // 提交事务
         session2.close();
     }
 
     //delete()方法
     @Test
     public void testDeleteStudent(){
         Student student=(Student)session.load(Student.class, Long.valueOf(1));
         session.delete(student);
     }
 }