时间:2021-07-01 10:21:17 帮助过:14人阅读
Hibernate关联关系可分为单向关联和双向关联两大类。单向关联可以分为一对一、一对多、多对一和多对多4种关联方式,而多向关联可以分为一对一、一对多和多对多3种关联方式。 Hibernate连接管理类HibernateUtil.java public class HibernateUtil { private st
Hibernate关联关系可分为单向关联和双向关联两大类。单向关联可以分为一对一、一对多、多对一和多对多4种关联方式,而多向关联可以分为一对一、一对多和多对多3种关联方式。
Hibernate连接管理类HibernateUtil.java
public class HibernateUtil {
private static SessionFactory sessionFactory;
private static final ThreadLocal threadLocal = new ThreadLocal();
static{
try{
Configuration cfg = new Configuration().configure();
sessionFactory = cfg.buildSessionFactory();
}catch(Throwable ex){
throw new ExceptionInInitializerError(ex);
}
}
public static SessionFactory getSessionFactory(){
return sessionFactory;
}
public static Session getSession() throws HibernateException{
Session session = (Session)threadLocal.get();
if(session == null || !session.isOpen()){
session = (sessionFactory != null)?sessionFactory.openSession():null;
threadLocal.set(session);
}
return session;
}
public static void closeSession() throws HibernateException{
Session session = (Session)threadLocal.get();
threadLocal.set(null);
if(session != null){
session.close();
}
}
public static void shutdown(){
getSessionFactory().close();
}
}
1.单向的一对一关联
(1)通过主键关联
通过主键关联,是指两个数据表之间通过主键建立一对一的关联关系。这两张表的主键值是相同的,一张表改动时,另一张也会相关的发生改变,从而避免多余字段被创建,但基于主键关联的持久化类(其对应的数据表称为从表)不能拥有自己的主键生成策略,它的主键由关联类负责生成。另外,增加one-to-one元素来关联属性,必须为one-to-one元素增加constrained=”true”属性,表明该类主键由关联类生成。
示例:
实体类:
User.java
public class User {
private int userid;
private String name;
private String password;
private Address address;
public int getUserid() {
return userid;
}
public void setUserid(int userid) {
this.userid = userid;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
}
Address.java
public class Address {
private int addressid;
private String addressinfo;
public int getAddressid() {
return addressid;
}
public void setAddressid(int addressid) {
this.addressid = addressid;
}
public String getAddressinfo() {
return addressinfo;
}
public void setAddressinfo(String addressinfo) {
this.addressinfo = addressinfo;
}
}
表结构:
user表:
address表:
配置文件:
User.hbm.xml
<class name="com.entity.User" table="user">
<id name="id" type="java.lang.Integer" column="user_id">
class="foreign">
name="property">address
id>
<property name="name" type="java.lang.String" column="name">
property>
<property name="password" type="java.lang.String" column="password">
property>
to-one name="address" class="Address" constrained="true"> to-one>
class>
Address.hbm.xml
<class name="com.entity.Address" table="address">
<id name="addressid" type="java.lang.Integer" column="addressid">
class="identity"/>
id>
<property name="addressinfo" type="java.lang.String" column="addressinfo">
property>
class>
测试类Test.java
public class Test {
public static void main(String[] args){
Session session = HibernateUtil.getSession();
Transaction tx = session.beginTransaction();
User u = new User();
u.setName("sbw");
u.setPassword("123");
Address a = new Address();
a.setAddressinfo("heu");
u.setAddress(a);
session.save(a);
session.save(u);
tx.commit();
HibernateUtil.closeSession();
}
}
运行结果:
(2)通过外键关联
通过外键关联时两张数据表的主键是不同的,通过在一张表中添加外键列来保持一对一的关系。配置外键关联关系时需要使用many-to-one元素。因为通过外键关联的一对一关系,本质上是多对一关系的特例。因此,只需在many-to-one元素中增加unique=“true”属性即可,这相当于在多的一端增加了唯一性的约束,表示多的一端也必须是唯一的,这样就变成为单向的一对一关系了。
示例:
实体类与通过主键关联相同。
表结构:
user表
address表
配置文件:
User.hbm.xml
<class name="com.entity.User" table="user">
<id name="userid" type="java.lang.Integer" column="userid">
class="identity"/>
id>
<property name="name" type="java.lang.String" column="name">
property>
<property name="password" type="java.lang.String" column="password">
property>
to-one name="address" class="com.entity.Address" unique="true" column="addressid"> to-one>
class>
Address.hbm.xml
<class name="com.entity.Address" table="address">
<id name="addressid" type="java.lang.Integer" column="addressid">
class="identity"/>
id>
<property name="addressinfo" type="java.lang.String" column="addressinfo">
property>
class>
测试类与通过主键关联一样
运行结果:
2.单向一对多关联
单向的一对多关联映射关系主要是通过外键来关联的。一对多的关联映射是在表示多的一方的数据表中增加一个外键,并由“一”的一方指向“多”的一方。单向的一对多关联的持久化类里需要包含一个集合属性,在“一”的一方访问“多”的一方时,“多”的一方将以集合的形式来体现。
示例:
实体类:
User.java
public class User {
private int userid;
private String name;
private String password;
private Set address = new HashSet();
public int getUserid() {
return userid;
}
public void setUserid(int userid) {
this.userid = userid;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public Set getAddress() {
return address;
}
public void setAddress(Set address) {
this.address = address;
}
}
Address.java
public class Address {
private int addressid;
private String addressinfo;
public int getAddressid() {
return addressid;
}
public void setAddressid(int addressid) {
this.addressid = addressid;
}
public String getAddressinfo() {
return addressinfo;
}
public void setAddressinfo(String addressinfo) {
this.addressinfo = addressinfo;
}
}
表结构:
User表
Address表
配置文件
User.hbm.xml
<class name="com.entity.User" table="user">
<id name="userid" type="java.lang.Integer" column="userid">
class="identity"/>
id>
<property name="name" type="java.lang.String" column="name">
property>
<property name="password" type="java.lang.String" column="password">
property>
<set name="address" table="address" inverse="false" lazy="true">
name="userid"/>
to-many class="com.entity.User"/>
set>
class>
Address.hbm.xml
<class name="com.entity.Address" table="address">
<id name="addressid" type="java.lang.Integer" column="addressid">
class="identity"/>
id>
<property name="addressinfo" type="java.lang.String" column="addressinfo">
property>
class>
测试代码
Test.java
public class Test {
public static void main(String[] args){
Session session = HibernateUtil.getSession();
Transaction tx = session.beginTransaction();
User u = new User();
u.setName("sbw");
u.setPassword("123");
Address a = new Address();
a.setAddressinfo("heu");
Address a1 = new Address();
a1.setAddressinfo("hrb");
u.getAddress().add(a);
u.getAddress().add(a1);
session.save(a);
session.save(a1);
session.save(u);
tx.commit();
HibernateUtil.closeSession();
}
}
运行结果:
3.单向的多对一关联
单向的多对一关联映射关系也是通过外键来关联的。多对一的映射方式类似于一对多的映射方式,不过它的映射关系是由“多”的一方指向“一”的一方。在表示“多”的一方的数据表中增加一个外键来指向表示“一”的一方的数据表,“一”的一方作为主表,”多“的一方作为从表。
示例:
实体类
User.java
public class User {
private int userid;
private String name;
private String password;
private Address address = new Address();
public int getUserid() {
return userid;
}
public void setUserid(int userid) {
this.userid = userid;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
}
Address.java
public class Address {
private int addressid;
private String addressinfo;
public int getAddressid() {
return addressid;
}
public void setAddressid(int addressid) {
this.addressid = addressid;
}
public String getAddressinfo() {
return addressinfo;
}
public void setAddressinfo(String addressinfo) {
this.addressinfo = addressinfo;
}
}
表结构:
user表
address表
配置文件:
User.hbm.xml
<class name="com.entity.User" table="user">
<id name="userid" type="java.lang.Integer" column="userid">
class="identity"/>
id>
<property name="name" type="java.lang.String" column="name">
property>
<property name="password" type="java.lang.String" column="password">
property>
to-one name="address" column="addressid"/>
class>
Address.hbm.xml
<class name="com.entity.Address" table="address">
<id name="addressid" type="java.lang.Integer" column="addressid">
class="identity"/>
id>
<property name="addressinfo" type="java.lang.String" column="addressinfo">
property>
class>
测试类Test.java
public class Test {
public static void main(String[] args){
Session session = HibernateUtil.getSession();
Transaction tx = session.beginTransaction();
User u = new User();
u.setName("sbw");
u.setPassword("123");
User u1 = new User();
u.setName("gaoya");
u.setPassword("456");
Address a = new Address();
a.setAddressinfo("heu");
u.setAddress(a);
u1.setAddress(a);
session.save(a);
session.save(u);
session.save(u1);
tx.commit();
HibernateUtil.closeSession();
}
}
测试结果:
4.单向的多对多关联
多对多关联在数据库中是比较常见的,它利用中间表将两个主表关联起来。中间表的作用是将两张表的主键作为其外键,通过外键建立这两张表的映射关系。在单向的多对多关联中,需要在主控端的类定义中增加一个Set集合属性,使得被关联一方的类的实例以集合的形式存在。
示例:
实体类:
User.java
public class User {
private int userid;
private String name;
private String password;
private Set address = new HashSet();
public int getUserid() {
return userid;
}
public void setUserid(int userid) {
this.userid = userid;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public Set getAddress() {
return address;
}
public void setAddress(Set address) {
this.address = address;
}
}
Address.java
public class Address {
private int addressid;
private String addressinfo;
public int getAddressid() {
return addressid;
}
public void setAddressid(int addressid) {
this.addressid = addressid;
}
public String getAddressinfo() {
return addressinfo;
}
public void setAddressinfo(String addressinfo) {
this.addressinfo = addressinfo;
}
}
表结构:
user表:
user_address表:
address表:
配置文件:
User.hbm.xml
<class name="com.entity.User" table="user">
<id name="userid" type="java.lang.Integer" column="userid">
class="identity"/>
id>
<property name="name" type="java.lang.String" column="name">
property>
<property name="password" type="java.lang.String" column="password">
property>
<set name="address" table="user_address">
"userid"/>
to-many column="addressid" class="com.entity.Address"/>
set>
class>
Address.hbm.xml
<class name="com.entity.Address" table="address">
<id name="addressid" type="java.lang.Integer" column="addressid">
class="identity"/>
id>
<property name="addressinfo" type="java.lang.String" column="addressinfo">
property>
class>
测试代码Test.java
public class Test {
public static void main(String[] args){
Session session = HibernateUtil.getSession();
Transaction tx = session.beginTransaction();
User u = new User();
u.setName("sbw");
u.setPassword("123");
User u1 = new User();
u1.setName("gaoya");
u1.setPassword("456");
Address a = new Address();
a.setAddressinfo("heu");
Address a1 = new Address();
a1.setAddressinfo("hrb");
u.getAddress().add(a);
u.getAddress().add(a1);
u1.getAddress().add(a);
u1.getAddress().add(a1);
session.save(a);
session.save(a1);
session.save(u);
session.save(u1);
tx.commit();
HibernateUtil.closeSession();
}
}
测试结果: