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：