hibernate一对多关联映射（二）－－－双向关联
2008-12-02 09:53
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1.新建工程项目hibernate_one2many_2,在该项目下添加hibernate所需的Jar包和数据库mysql驱动Jar包。
2.编写工具类HibernateUtils和ExportDB,代码如下：
HibernateUtils.java
package com.i51pro.hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtils {
private static SessionFactory sessionFactory;
static {
try {
Configuration cfg = new Configuration().configure();
sessionFactory = cfg.buildSessionFactory();
} catch (Exception e) {
e.printStackTrace();
}
}
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
public static Session getSession() {
return sessionFactory.openSession();
}
public static void closeSession(Session session) {
if (session != null) {
if (session.isOpen()) {
session.close();
}
}
}
}
ExportDB.java
package com.i51pro.hibernate;
import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
public class ExportDB {
/**
* @param args
*/
public static void main(String[] args) {
Configuration cfg = new Configuration().configure();
SchemaExport export = new SchemaExport(cfg);
export.create(true, true);
}
}
3.编写实体类和映射文件，代码如下：
Student.java
package com.i51pro.hibernate;
public class Student {
private int id;
private String name;
private Classes classes;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Classes getClasses() {
return classes;
}
public void setClasses(Classes classes) {
this.classes = classes;
}
}
<
4000
/span>
Classes.java
package com.i51pro.hibernate;
import java.util.Set;
public class Classes {
private int id;
private String name;
private Set students;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set getStudents() {
return students;
}
public void setStudents(Set students) {
this.students = students;
}
}
Student.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.i51pro.hibernate.Student" table="t_student">
<id name="id">
<generator class="native"/>
</id>
<property name="name" />
<many-to-one name="classes" column="classesid" />
</class>
</hibernate-mapping>
Classes.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.i51pro.hibernate.Classes" table="t_classes">
<id name="id">
<generator class="native" />
</id>
<property name="name"/>
<set name="students" inverse="true" cascade="all">
<key column="classesid" />
<one-to-many class="com.i51pro.hibernate.Student"/>
</set>
</class>
</hibernate-mapping>
4.编写hibernate映射文件，代码如下：
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_one2many_2</property>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">admin</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.show_sql">true</property>
<mapping resource="com/i51pro/hibernate/Student.hbm.xml"/>
<mapping resource="com/i51pro/hibernate/Classes.hbm.xml"/>
</session-factory>
</hibernate-configuration>
4.在工程项目hibernate_one2many_2下，建立SourceFolder,命名为test,在该包下编写测试类One2ManyTest，进行单元测试，代码如下：
package com.i51pro.hibernate;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.Transaction;
import junit.framework.TestCase;
public class One2ManyTest extends TestCase {
public void testSave1() {
Session session = null;
try {
session = HibernateUtils.getSession();
Transaction tx = session.beginTransaction();
Student student1 = new Student();
student1.setName("学生1");
session.save(student1);
Student student2 = new Student();
student2.setName("学生2");
session.save(student2);
Set students = new HashSet();
students.add(student1);
students.add(student2);
Classes classes = new Classes();
classes.setName("JAVA学习小组");
classes.setStudents(students);
//可以保存
session.save(classes);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave2() {
Session session = null;
try {
session = HibernateUtils.getSession();
Transaction tx = session.beginTransaction();
Classes classes = new Classes();
classes.setName("JAVA研发小组");
session.save(classes);
Student student1 = new Student();
student1.setName("程序员1");
student1.setClasses(classes);
session.save(student1);
Student student2 = new Student();
student2.setName("程序员2");
student2.setClasses(classes);
session.save(student2);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave3() {
Session session = null;
try {
session = HibernateUtils.getSession();
Transaction tx = session.beginTransaction();
Classes classes = new
b9b5
Classes();
classes.setName("JAVA研发开小组");
Student student1 = new Student();
student1.setName("程序员1");
student1.setClasses(classes);
Student student2 = new Student();
student2.setName("程序员2");
student2.setClasses(classes);
Set students = new HashSet();
students.add(student1);
students.add(student2);
classes.setStudents(students);
//可以正确保存
session.save(classes);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Classes classes = (Classes)session.load(Classes.class, 2);
System.out.println("classes.name=" + classes.getName());
Set students = classes.getStudents();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println("student.name=" + student.getName());
}
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Student student = (Student)session.load(Student.class, 1);
System.out.println("student.name=" + student.getName());
System.out.println("student.classes.name=" + student.getClasses().getName());
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
}
总结：hihernate一对多关联映射（双向Classes<----->Student）
一对多双向关联映射：
* 在一一端的集合上使用<key>，在对方表中加入一个外键指向一一端
* 在多一端采用<many-to-one>
注意：<key>标签指定的外键字段必须和<many-to-one>指定的外键字段一致，否则引用字段的错误
如果在”一“一端维护一对多关联关系，hibernate会发出多余的udpate语句，所以我们一般在多
的一端来维护关联关系
关于inverse属性：
inverse主要用在一对多和多对多双向关联上，inverse可以被设置到集合标签<set>上，
默认inverse为false，所以我们可以从”一“一端和”多“一端维护关联关系，
如果设置成inverse为true，则我们只能从多一端来维护关联关系
注意：inverse属性，只影响数据的存储，也就是持久化
inverse和cascade
* inverse是关联关系的控制方向
* cascade操作上的连锁反应
2.编写工具类HibernateUtils和ExportDB,代码如下：
HibernateUtils.java
package com.i51pro.hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtils {
private static SessionFactory sessionFactory;
static {
try {
Configuration cfg = new Configuration().configure();
sessionFactory = cfg.buildSessionFactory();
} catch (Exception e) {
e.printStackTrace();
}
}
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
public static Session getSession() {
return sessionFactory.openSession();
}
public static void closeSession(Session session) {
if (session != null) {
if (session.isOpen()) {
session.close();
}
}
}
}
ExportDB.java
package com.i51pro.hibernate;
import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
public class ExportDB {
/**
* @param args
*/
public static void main(String[] args) {
Configuration cfg = new Configuration().configure();
SchemaExport export = new SchemaExport(cfg);
export.create(true, true);
}
}
3.编写实体类和映射文件，代码如下：
Student.java
package com.i51pro.hibernate;
public class Student {
private int id;
private String name;
private Classes classes;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Classes getClasses() {
return classes;
}
public void setClasses(Classes classes) {
this.classes = classes;
}
}
<
4000
/span>
Classes.java
package com.i51pro.hibernate;
import java.util.Set;
public class Classes {
private int id;
private String name;
private Set students;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set getStudents() {
return students;
}
public void setStudents(Set students) {
this.students = students;
}
}
Student.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.i51pro.hibernate.Student" table="t_student">
<id name="id">
<generator class="native"/>
</id>
<property name="name" />
<many-to-one name="classes" column="classesid" />
</class>
</hibernate-mapping>
Classes.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.i51pro.hibernate.Classes" table="t_classes">
<id name="id">
<generator class="native" />
</id>
<property name="name"/>
<set name="students" inverse="true" cascade="all">
<key column="classesid" />
<one-to-many class="com.i51pro.hibernate.Student"/>
</set>
</class>
</hibernate-mapping>
4.编写hibernate映射文件，代码如下：
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_one2many_2</property>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">admin</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.show_sql">true</property>
<mapping resource="com/i51pro/hibernate/Student.hbm.xml"/>
<mapping resource="com/i51pro/hibernate/Classes.hbm.xml"/>
</session-factory>
</hibernate-configuration>
4.在工程项目hibernate_one2many_2下，建立SourceFolder,命名为test,在该包下编写测试类One2ManyTest，进行单元测试，代码如下：
package com.i51pro.hibernate;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.Transaction;
import junit.framework.TestCase;
public class One2ManyTest extends TestCase {
public void testSave1() {
Session session = null;
try {
session = HibernateUtils.getSession();
Transaction tx = session.beginTransaction();
Student student1 = new Student();
student1.setName("学生1");
session.save(student1);
Student student2 = new Student();
student2.setName("学生2");
session.save(student2);
Set students = new HashSet();
students.add(student1);
students.add(student2);
Classes classes = new Classes();
classes.setName("JAVA学习小组");
classes.setStudents(students);
//可以保存
session.save(classes);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave2() {
Session session = null;
try {
session = HibernateUtils.getSession();
Transaction tx = session.beginTransaction();
Classes classes = new Classes();
classes.setName("JAVA研发小组");
session.save(classes);
Student student1 = new Student();
student1.setName("程序员1");
student1.setClasses(classes);
session.save(student1);
Student student2 = new Student();
student2.setName("程序员2");
student2.setClasses(classes);
session.save(student2);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave3() {
Session session = null;
try {
session = HibernateUtils.getSession();
Transaction tx = session.beginTransaction();
Classes classes = new
b9b5
Classes();
classes.setName("JAVA研发开小组");
Student student1 = new Student();
student1.setName("程序员1");
student1.setClasses(classes);
Student student2 = new Student();
student2.setName("程序员2");
student2.setClasses(classes);
Set students = new HashSet();
students.add(student1);
students.add(student2);
classes.setStudents(students);
//可以正确保存
session.save(classes);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Classes classes = (Classes)session.load(Classes.class, 2);
System.out.println("classes.name=" + classes.getName());
Set students = classes.getStudents();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println("student.name=" + student.getName());
}
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Student student = (Student)session.load(Student.class, 1);
System.out.println("student.name=" + student.getName());
System.out.println("student.classes.name=" + student.getClasses().getName());
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
}
总结：hihernate一对多关联映射（双向Classes<----->Student）
一对多双向关联映射：
* 在一一端的集合上使用<key>，在对方表中加入一个外键指向一一端
* 在多一端采用<many-to-one>
注意：<key>标签指定的外键字段必须和<many-to-one>指定的外键字段一致，否则引用字段的错误
如果在”一“一端维护一对多关联关系，hibernate会发出多余的udpate语句，所以我们一般在多
的一端来维护关联关系
关于inverse属性：
inverse主要用在一对多和多对多双向关联上，inverse可以被设置到集合标签<set>上，
默认inverse为false，所以我们可以从”一“一端和”多“一端维护关联关系，
如果设置成inverse为true，则我们只能从多一端来维护关联关系
注意：inverse属性，只影响数据的存储，也就是持久化
inverse和cascade
* inverse是关联关系的控制方向
* cascade操作上的连锁反应
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