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.双向的一对一关联

（1）通过主键关联

通过主键关联的双向一对一映射，在需要一方的配置文件中将主键生成策略配置成foreign，即表示需要根据另一方的主键来生成自己的主键，而该实体本身不具有自己的主键生成策略。

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;
 private User user;

 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;
 }
 public User getUser() {
 return user;
 }
 public void setUser(User user) {
 this.user = user;
 } 

}

表结构：

User表

Address表

配置文件：

Use.hbm.xml

Address.hbm.xml

 >
 
 
 user
 
 

 
 

 

 

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");

 a.setUser(u);
 u.setAddress(a);


 session.save(u);
 session.save(a);
 tx.commit();

 HibernateUtil.closeSession();

 }
}

测试结果：

（2）通过外键关联

通过外键关联的双向一对一映射，外键可以放在任意一方。在存放外键一方的映射文件中，需要添加many-to-one元素，并为该元素添加unique=“true”属性。而另一方的配置文件中要添加one-to-one元素，并使用其name属性来指定关联属性名。此时，存放外键的一方对应的数据表为从表，而另一方对应的数据表变为主表。

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

Address.hbm.xml

测试类与通过主键关联一样

测试结果：

2.双向的一对多关联(与双向多对一完全相同)

双向的一对多关联在“多”的一方要增加新属性以引用关联实体，在“一”的一方则增加集合属性，该集合中包含“多”的一方的关联实体。

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;
 private User user;

 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;
 }
 public User getUser() {
 return user;
 }
 public void setUser(User user) {
 this.user = user;
 } 

}

表结构：

user表

address表

配置文件

User.hbm.xml

Address.hbm.xml

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");
 Address a1 = new Address();
 a.setAddressinfo("hrb");

 a.setUser(u);
 a1.setUser(u);

 u.getAddress().add(a);
 u.getAddress().add(a1);

 session.save(a);
 session.save(a1);
 session.save(u);
 tx.commit();

 HibernateUtil.closeSession();

 }
}

测试结果：

3.双向的多对多关联

在双向的多对多关联中，两端都要添加Set集合属性。要实现双向的多对多关联，必须使用中间表来实现两个实体间的关联关系。

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;
 private Set user = new HashSet();

 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;
 }
 public Set getUser() {
 return user;
 }
 public void setUser(Set user) {
 this.user = user;
 } 

}

表结构：

user表

address表

user_address表

配置文件

User.hbm.xml:

Address.hbm.xml

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();
 u1.setName("gaoya");
 u1.setPassword("456");

 Address a = new Address();
 a.setAddressinfo("heu");
 Address a1 = new Address();
 a1.setAddressinfo("hrb");

 a.getUser().add(u);
 a.getUser().add(u1);
 a1.getUser().add(u);
 a1.getUser().add(u1);

 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：