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：