Hibernate关联关系映射(双向篇)

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<Session> threadLocal = new ThreadLocal<Session>();

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

<hibernate-mapping>
<class name="com.entity.User" table="user">
<id name="userid" type="java.lang.Integer" column="userid">
<generator class="identity"/>
</id>

<property name="name" type="java.lang.String" column="name">
</property>
<property name="password" type="java.lang.String" column="password">
</property>

<one-to-one name="address" class="com.entity.Address" cascade="all"/>

</class>
</hibernate-mapping>

Address.hbm.xml

<hibernate-mapping>
<class name="com.entity.Address" table="address"<span>>
<id name="addressid" type="java.lang.Integer" column="addressid">
<generator class="foreign">
<param name="property">user</param>
</generator>
</id>

<property name="addressinfo" type="java.lang.String" column="addressinfo">
</property>

<one-to-one name="user" class="com.entity.User" constrained="true"/>

</class>
</hibernate-mapping>

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

<hibernate-mapping>
<class name="com.entity.User" table="user">
<id name="userid" type="java.lang.Integer" column="userid">
<generator class="identity"/>
</id>

<property name="name" type="java.lang.String" column="name">
</property>
<property name="password" type="java.lang.String" column="password">
</property>

<one-to-one name="address" cascade="all"/>

</class>
</hibernate-mapping>

Address.hbm.xml

<hibernate-mapping>
<class name="com.entity.Address" table="address">
<id name="addressid" type="java.lang.Integer" column="addressid">
<generator class="identity">
</generator>
</id>

<property name="addressinfo" type="java.lang.String" column="addressinfo">
</property>

<many-to-one name="user" class="com.entity.User" unique="true">
<column name="userid"/>
</many-to-one>

</class>
</hibernate-mapping>

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> address = new HashSet<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 Set<Address> getAddress() {
return address;
}
public void setAddress(Set<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

User.hbm.xml

<hibernate-mapping>
<class name="com.entity.User" table="user">
<id name="userid" type="java.lang.Integer" column="userid">
<generator 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="true" lazy="true">
<key>
<column name="userid"/>
</key>

<one-to-many class="com.entity.Address"/>
</set>

</class>
</hibernate-mapping>

Address.hbm.xml

<hibernate-mapping>
<class name="com.entity.Address" table="address">
<id name="addressid" type="java.lang.Integer" column="addressid">
<generator class="identity">
</generator>
</id>

<property name="addressinfo" type="java.lang.String" column="addressinfo">
</property>

<many-to-one name="user" class="com.entity.User" unique="true">
<column name="userid"/>
</many-to-one>

</class>
</hibernate-mapping>

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> address = new HashSet<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 Set<Address> getAddress() {
return address;
}
public void setAddress(Set<Address> address) {
this.address = address;
}
}

Address.java

public class Address {
private int addressid;
private String addressinfo;
private Set<User> user = new HashSet<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 Set<User> getUser() {
return user;
}
public void setUser(Set<User> user) {
this.user = user;
}

}

表结构：

user表



address表



user_address表



配置文件

User.hbm.xml:

<hibernate-mapping>
<class name="com.entity.User" table="user">
<id name="userid" type="java.lang.Integer" column="userid">
<generator 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" inverse="true">
<key>
<column name="userid"/>
</key>

<many-to-many class="com.entity.Address" column="addressid"/>
</set>

</class>
</hibernate-mapping>

Address.hbm.xml

<hibernate-mapping>
<class name="com.entity.Address" table="address">
<id name="addressid" type="java.lang.Integer" column="addressid">
<generator class="identity">
</generator>
</id>

<property name="addressinfo" type="java.lang.String" column="addressinfo">
</property>

<set name="user" table="user_address">
<key>
<column name="addressid"/>
</key>

<many-to-many class="com.entity.User" column="userid"/>
</set>

</class>
</hibernate-mapping>

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：