@OneToMany单向一对多

Hibernate单项一对多详细配置：

数据模型：



一个年级有多个学生，每个学生只属于一个年级。

用hibernate实现一对多关系有xml配置和注解两种方式，下面逐一介绍：

第一种：注解方式

Grade.java

package cn.siggy.pojo;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.MappedSuperclass;
import javax.persistence.OneToMany;
import javax.persistence.Table;
/**
* AbstractGrade entity provides the base persistence definition of the Grade
* entity. @author MyEclipse Persistence Tools
*/
@Entity
@Table(name = "GRADE")
public class Grade implements java.io.Serializable {

// Fields

private Integer id;
private String name;
private Set<Student> students = new HashSet<Student>(0);

// Constructors
public Grade() {
super();
// TODO Auto-generated constructor stub
}

public Grade(Integer id, String name, Set<Student> students) {
super();
this.id = id;
this.name = name;
this.students = students;
}

// Property accessors
@Id
@GeneratedValue
@Column(name = "ID", unique = true, nullable = false, precision = 10, scale = 0)
public Integer getId() {
return this.id;
}

public void setId(Integer id) {
this.id = id;
}

@Column(name = "NAME")
public String getName() {
return this.name;
}

public void setName(String name) {
this.name = name;
}

@OneToMany(cascade=CascadeType.ALL,fetch=FetchType.LAZY,targetEntity=Student.class)
//@JoinColumn(name="GRADE_ID",nullable=true) //该配置在单独保存Grade是会将student中的外键字段置空，所以采用下面配置
@JoinColumn(name="PLAN_ID",updatable=false)
public Set<Student> getStudents() {
return this.students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
}

Student.java

package cn.siggy.pojo;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.MappedSuperclass;
import javax.persistence.Table;

/**
* AbstractStudent entity provides the base persistence definition of the
* Student entity. @author MyEclipse Persistence Tools
*/
@Entity
@Table(name = "STUDENT")
public class Student implements java.io.Serializable {

// Fields

private Integer id;
private String name;
private Integer age;

// Constructors

/** default constructor */
public Student() {
}

// Property accessors
@Id
@GeneratedValue
@Column(name = "ID", unique = true, nullable = false, precision = 10, scale = 0)
public Integer getId() {
return this.id;
}

public void setId(Integer id) {
this.id = id;
}

@Column(name = "NAME", length = 510)
public String getName() {
return this.name;
}

public void setName(String name) {
this.name = name;
}

@Column(name = "AGE", precision = 10, scale = 0)
public Integer getAge() {
return this.age;
}

public void setAge(Integer age) {
this.age = age;
}

}

hibernate.cfg.xml

<!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>
<!--数据库信息  -->
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<property name="connection.url">jdbc:oracle:thin:@10.18.100.126:1521:gsdb</property>
<property name="connection.username">db_lzsmw</property>
<property name="connection.password">pass_lzsmw</property>
<!--hibernate可选项 -->
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<property name="hbm2ddl.auto">update</property>
<!-- hbm文件 --><!--
<mapping resource="cn/siggy/pojo/Student.hbm.xml"/>
<mapping resource="cn/siggy/pojo/Grade.hbm.xml"/>
-->
<!-- 使用注解 -->
<mapping class="cn.siggy.pojo.Grade"/>
<mapping class="cn.siggy.pojo.Student"/>
</session-factory>
</hibernate-configuration>

 

第二种：xml配置方式实现一对多 

Grade.java

package cn.siggy.pojo;

import java.util.HashSet;
import java.util.Set;

public class Grade {
private int id;
private String name;
private Set<Student> students = new HashSet<Student>(0);
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<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
}

Grade.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="cn.siggy.pojo">
<class name="Grade">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name"/>
<!-- set是 Grade中的集合属性  name属性名称 -->
<set name="students">
<!-- key表示外键  column外键列名-->
<key column="grade_id" not-null="true"></key>
<!-- one-to-many 一对多  类Grade 中  students 所表示类型 -->
<one-to-many class="Student"/>
</set>
</class>
</hibernate-mapping>

Student.java

package cn.siggy.pojo;

public class Student {
private int id;
private String name;
private int age;
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 int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}

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="cn.siggy.pojo">
<class name="Student">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name"/>
<property name="age"/>
</class>
</hibernate-mapping>

hibernate.cfg.xml

<!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>
<!--数据库信息  -->
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<property name="connection.url">jdbc:oracle:thin:@10.18.100.126:1521:gsdb</property>
<property name="connection.username">db_lzsmw</property>
<property name="connection.password">pass_lzsmw</property>
<!--hiberna
4000
te可选项 -->
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<property name="hbm2ddl.auto">update</property>
<!-- hbm文件 -->
<mapping resource="cn/siggy/pojo/Student.hbm.xml"/>
<mapping resource="cn/siggy/pojo/Grade.hbm.xml"/>

<!-- 使用注解 -->
<!--<mapping class="cn.siggy.pojo.Grade"/>
<mapping class="cn.siggy.pojo.Student"/>-->
</session-factory>
</hibernate-configuration>

工具类：HibernateUtil.java

package cn.siggy.util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
private static Configuration cfg=null;
private static SessionFactory factory=null;
private static Session session = null;
static{
cfg = new Configuration().configure();
factory = cfg.buildSessionFactory(new StandardServiceRegistryBuilder()
.applySettings(cfg.getProperties()).build());
}
public static Session getSession(){
if(factory!=null)
return factory.openSession();
factory=cfg.buildSessionFactory(new StandardServiceRegistryBuilder()
.applySettings(cfg.getProperties()).build());
return factory.openSession();
}
public static void closeSession(){
if(session!=null&&session.isOpen())
session.close();
}
}

Junit单元测试类：

package cn.siggy.test;

import java.sql.SQLException;
import java.util.Iterator;
import javax.sql.rowset.serial.SerialException;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.Test;
import cn.siggy.pojo.Grade;
import cn.siggy.pojo.Student;
import cn.siggy.util.HibernateUtil;

public class HibernateTest {
@Test
public void testCreateDB(){
Configuration cfg = new Configuration().configure();
SchemaExport se = new SchemaExport(cfg);
//第一个参数 是否生成ddl脚本  第二个参数  是否执行到数据库中
se.create(true, true);
}
@Test
public void testSave() throws HibernateException, SerialException, SQLException{
Session session = null;
Transaction tx = null;
try{
session = HibernateUtil.getSession();
tx = session.beginTransaction();
Grade grade = new Grade();
grade.setName("基础");

Student stu = new Student();
stu.setName("张三疯");
stu.setAge(22);
Student stu1 = new Student();
stu1.setName("老王");
stu1.setAge(23);
//关联
grade.getStudents().add(stu);
grade.getStudents().add(stu1);
//保存数据的顺序 是根据外键的配置来决定的
//如果外键不能为null,那么先保存一的一端
//如果外键可以为null,则可以随意保存
session.save(grade);
session.save(stu);
session.save(stu1);

tx.commit();

}catch (HibernateException e) {
if(tx!=null)
tx.rollback();
e.printStackTrace();
throw e;
}finally{
HibernateUtil.closeSession();
}
}
@Test
public void testGet(){
Session session = null;
Transaction tx = null;
try{
session = HibernateUtil.getSession();
tx = session.beginTransaction();
//取数据
Grade grade = (Grade)session.get(Grade.class, 1);
System.out.println("gradeName="+grade.getName());
System.out.println("grade所对应的多的一端的数据");
Iterator<Student> iter = grade.getStudents().iterator();
for(;iter.hasNext();){
Student temp = iter.next();
System.out.println("name="+temp.getName()+"\tage="+temp.getAge());
}
tx.commit();
}catch (HibernateException e) {
if(tx!=null)
tx.rollback();
e.printStackTrace();
throw e;
}finally{
HibernateUtil.closeSession();
}
}
}

如下表结构代码可以自动生成，所以不用手动创建

Student表结构：





Grade表结构：