（五）Hibernate 操作对象

时间 2021-01-05

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

 1 <?xml version='1.0' encoding='utf-8'?>
 2 <!DOCTYPE hibernate-configuration PUBLIC
 3         "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 4         "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 5 
 6 <hibernate-configuration>
 7 
 8     <session-factory>
 9 
10         <!--数据库连接设置 -->
11         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
12         <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
13         <property name="connection.username">root</property>
14         <property name="connection.password">123456</property>
15 
16        
17         <!-- 方言 -->
18         <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
19     
20         <!-- 控制台显示SQL -->
21         <property name="show_sql">true</property>
22 
23         <!-- 自动更新表结构 -->
24         <property name="hbm2ddl.auto">update</property>
25         
26           <mapping resource="com/wishwzp/model/Student.hbm.xml"/>
27           
28           <mapping resource="com/wishwzp/model/Class.hbm.xml"/>
29 
30     </session-factory>
31 
32 </hibernate-configuration>

Class.java

 1 package com.wishwzp.model;
 2 
 3 public class Class {
 4 
 5     private long id;
 6     private String name;
 7     
 8     public long getId() {
 9         return id;
10     }
11     public void setId(long id) {
12         this.id = id;
13     }
14     public String getName() {
15         return name;
16     }
17     public void setName(String name) {
18         this.name = name;
19     }
20     
21     
22 }

Class.hbm.xml

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC
 3         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5 
 6 <hibernate-mapping package="com.wishwzp.model">
 7 
 8     <class name="Class" table="t_class">
 9         <id name="id" column="classId">
10             <generator class="native"></generator>
11         </id>
12         
13         <property name="name" column="className"></property>
14     </class>
15 
16 </hibernate-mapping>

Student.java

 1 package com.wishwzp.model;
 2 
 3 public class Student {
 4 
 5     private long id;
 6     private String name;
 7     private Class c;
 8     
 9     public long getId() {
10         return id;
11     }
12     public void setId(long id) {
13         this.id = id;
14     }
15     public String getName() {
16         return name;
17     }
18     public void setName(String name) {
19         this.name = name;
20     }
21     
22     
23     public Class getC() {
24         return c;
25     }
26     public void setC(Class c) {
27         this.c = c;
28     }
29     @Override
30     public String toString() {
31         return "Student [id=" + id + ", name=" + name + "]";
32     }
33     
34     
35 }

Student.hbm.xml

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC
 3         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5 
 6 <hibernate-mapping package="com.wishwzp.model">
 7 
 8     <class name="Student" table="t_student">
 9         <id name="id" column="stuId">
10             <generator class="native"></generator>
11         </id>
12         
13         <property name="name" column="stuName"></property>
14         
15         <many-to-one name="c" column="classId" class="com.wishwzp.model.Class" cascade="save-update"></many-to-one>
16     </class>
17 
18 </hibernate-mapping>

StudentTest.java

 1 package com.wishwzp.service;
 2 
 3 import org.hibernate.Session;
 4 import org.hibernate.SessionFactory;
 5 
 6 import com.wishwzp.model.Class;
 7 import com.wishwzp.model.Student;
 8 import com.wishwzp.util.HibernateUtil;
 9 
10 public class StudentTest {
11     
12     public static void main(String[] args) {
13         SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
14         Session session=sessionFactory.openSession(); // 生成一个session
15         session.beginTransaction(); // 开启事务
16         
17         Class c1=new Class(); // 临时对象1
18         c1.setName("08计本");
19         
20         Class c2=new Class();  // 临时对象2
21         c2.setName("09计本");
22         
23         session.save(c1); // 持久化对象
24         session.save(c2); // 持久化对象
25         
26         session.delete(c2); // 删除对象
27         
28         session.getTransaction().commit(); // 提交事务
29         session.close(); // 关闭session
30         
31         System.out.println(c1.getName()); // 游离对象
32         System.out.println(c2.getName()); // 删除对象
33     }
34 }

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

 1 <?xml version='1.0' encoding='utf-8'?>
 2 <!DOCTYPE hibernate-configuration PUBLIC
 3         "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 4         "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 5 
 6 <hibernate-configuration>
 7 
 8     <session-factory>
 9 
10         <!--数据库连接设置 -->
11         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
12         <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
13         <property name="connection.username">root</property>
14         <property name="connection.password">123456</property>
15 
16        
17         <!-- 方言 -->
18         <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
19     
20         <!-- 控制台显示SQL -->
21         <property name="show_sql">true</property>
22 
23         <!-- 自动更新表结构 -->
24         <property name="hbm2ddl.auto">update</property>
25         
26           <mapping resource="com/wishwzp/model/Student.hbm.xml"/>
27           
28           <mapping resource="com/wishwzp/model/Class.hbm.xml"/>
29 
30     </session-factory>
31 
32 </hibernate-configuration>

Class.java

 1 package com.wishwzp.model;
 2 
 3 import java.util.HashSet;
 4 import java.util.Set;
 5 
 6 public class Class {
 7 
 8     private long id;
 9     private String name;
10     private Set<Student> students=new HashSet<Student>();
11     
12     public long getId() {
13         return id;
14     }
15     public void setId(long id) {
16         this.id = id;
17     }
18     public String getName() {
19         return name;
20     }
21     public void setName(String name) {
22         this.name = name;
23     }
24     public Set<Student> getStudents() {
25         return students;
26     }
27     public void setStudents(Set<Student> students) {
28         this.students = students;
29     }
30     
31     
32 }

Class.hbm.xml

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC
 3         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5 
 6 <hibernate-mapping package="com.wishwzp.model">
 7 
 8     <class name="Class" table="t_class">
 9         <id name="id" column="classId">
10             <generator class="native"></generator>
11         </id>
12         
13         <property name="name" column="className"></property>
14         
15         <set name="students" cascade="delete" inverse="true">
16             <key column="classId"></key>
17             <one-to-many class="com.wishwzp.model.Student"/>
18         </set>
19     </class>
20 
21 </hibernate-mapping>

Student.java

 1 package com.wishwzp.model;
 2 
 3 public class Student {
 4 
 5     private long id;
 6     private String name;
 7     private Class c;
 8     
 9     public long getId() {
10         return id;
11     }
12     public void setId(long id) {
13         this.id = id;
14     }
15     public String getName() {
16         return name;
17     }
18     public void setName(String name) {
19         this.name = name;
20     }
21     
22     
23     public Class getC() {
24         return c;
25     }
26     public void setC(Class c) {
27         this.c = c;
28     }
29     @Override
30     public String toString() {
31         return "Student [id=" + id + ", name=" + name + "]";
32     }
33     
34     
35 }

Studnet.hbm.xml

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC
 3         "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4         "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5 
 6 <hibernate-mapping package="com.wishwzp.model">
 7 
 8     <class name="Student" table="t_student">
 9         <id name="id" column="stuId">
10             <generator class="native"></generator>
11         </id>
12         
13         <property name="name" column="stuName"></property>
14         
15         <many-to-one name="c" column="classId" class="com.wishwzp.model.Class" cascade="save-update"></many-to-one>
16     </class>
17 
18 </hibernate-mapping>

StudentTest.java

  1 package com.wishwzp.service;
  2 
  3 import java.util.Iterator;
  4 import java.util.Set;
  5 
  6 import org.hibernate.Session;
  7 import org.hibernate.SessionFactory;
  8 import org.junit.After;
  9 import org.junit.Before;
 10 import org.junit.Test;
 11 
 12 import com.wishwzp.model.Class;
 13 import com.wishwzp.model.Student;
 14 import com.wishwzp.util.HibernateUtil;
 15 
 16 public class StudentTest {
 17 
 18     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
 19     private Session session;
 20     
 21     @Before
 22     public void setUp() throws Exception {
 23         session=sessionFactory.openSession(); // 生成一个session
 24         session.beginTransaction(); // 开启事务
 25     }
 26 
 27     @After
 28     public void tearDown() throws Exception {
 29          session.getTransaction().commit(); // 提交事务
 30          session.close(); // 关闭session
 31     }
 32 
 33     //save()方法
 34     @Test
 35     public void testSaveClassAndStudent() {
 36         Class c=new Class();
 37         c.setName("08计本");
 38        
 39         Student s1=new Student();
 40         s1.setName("张三");
 41         s1.setC(c);
 42         
 43         Student s2=new Student();
 44         s2.setName("李四");
 45         s2.setC(c);
 46        
 47         session.save(s1);
 48         session.save(s2);
 49         
 50     }
 51     
 52     //load()方法和get()方法的区别
 53     //Load()方法会抛出异常，而get()方法返回null;
 54     @Test
 55     public void testLoadClass(){
 56         // Class c=(Class)session.load(Class.class, Long.valueOf(2));
 57         Class c=(Class)session.load(Class.class, Long.valueOf(1));
 58         System.out.println(c.getStudents());
 59     }
 60     
 61     
 62     @Test
 63     public void testGetClass(){
 64         // Class c=(Class)session.get(Class.class, Long.valueOf(2));
 65         Class c=(Class)session.get(Class.class, Long.valueOf(1));
 66         System.out.println(c.getStudents());
 67     }
 68     
 69     //update()方法
 70     @Test
 71     public void testUpdateClass(){
 72         Session session1=sessionFactory.openSession();
 73         session1.beginTransaction();
 74         Class c=(Class)session1.get(Class.class, Long.valueOf(1));
 75         session1.getTransaction().commit(); // 提交事务
 76         session1.close();
 77         
 78         Session session2=sessionFactory.openSession();
 79         session2.beginTransaction();
 80         c.setName("08计算机本科2");
 81         session2.update(c);
 82         session2.getTransaction().commit(); // 提交事务
 83         session2.close();
 84     }
 85     
 86     //saveOrUpdate()方法
 87     @Test
 88     public void testSaveOrUpdateClass(){
 89         Session session1=sessionFactory.openSession();
 90         session1.beginTransaction();
 91         Class c=(Class)session1.get(Class.class, Long.valueOf(1));
 92         session1.getTransaction().commit(); // 提交事务
 93         session1.close();
 94         
 95         Session session2=sessionFactory.openSession();
 96         session2.beginTransaction();
 97         c.setName("08计算机本科3");
 98         
 99         Class c2=new Class();
100         c2.setName("09计算机本科3");
101         session2.saveOrUpdate(c);
102         session2.saveOrUpdate(c2);
103         session2.getTransaction().commit(); // 提交事务
104         session2.close();
105     }
106     
107     //merge()方法
108     @Test
109     public void testMergeClass(){
110         Session session1=sessionFactory.openSession();
111         session1.beginTransaction();
112         Class c=(Class)session1.get(Class.class, Long.valueOf(1));
113         session1.getTransaction().commit(); // 提交事务
114         session1.close();
115         
116         Session session2=sessionFactory.openSession();
117         session2.beginTransaction();
118         
119         Class c2=(Class)session2.get(Class.class, Long.valueOf(1));
120         c.setName("08计算机本科4");
121     
122         session2.merge(c);
123 
124         session2.getTransaction().commit(); // 提交事务
125         session2.close();
126     }
127     
128     //delete()方法
129     @Test
130     public void testDeleteStudent(){
131         Student student=(Student)session.load(Student.class, Long.valueOf(1));
132         session.delete(student);
133     }
134 }