Hibernate一对多单向（双向）关联映射

（1）、编写配置文件

　　Hibernate通过读写默认的XML配置文件hibernate.cfg.xml加载数据库配置信息、代码如下：　

<hibernate-configuration>

 	<session-factory>

		<!-- 数据库驱动 -->

		<property name="connection.driver_class">com.mysql.jdbc.Driver</property>

		<!-- 数据库连接的URL -->

		<property name="connection.url">jdbc:mysql://localhost:3306/db_database14</property>

		<!-- 数据库连接用户名 -->

		<property name="connection.username">root</property>

		<!-- 数据库连接密码 -->

		<property name="connection.password"></property>

		<!-- Hibernate方言 -->

		<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

		<!-- 打印SQL语句 -->

		<property name="show_sql">true</property>

		<!-- 映射文件  -->

		<mapping resource="com/wgh/model/Book.hbm.xml" />

		<mapping resource="com/wgh/model/Category.hbm.xml" />

 	</session-factory>

 </hibernate-configuration>

（2）、编写持久化类

　　持久化类是Hibernate操作的对象、它与数据库中的数据表相对应

（双向）
/**

 * 图书类别持久化类

 */

public class Category {

    private Integer id;            //ID

    private String name;        //类别名称

    private Set<Book> books;    //Set集合（类别中的所有图书）

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public Set<Book> getBooks() {

        return books;

    }

    public void setBooks(Set<Book> books) {

        this.books = books;

    }

}

（单向）
/**

 * 图书类别持久化类

 */

public class Category {

    private Integer id;            //ID

    private String name;        //类别名称

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

}

/**

 * 图书持久类

 */

public class Book {

    private Integer id;            //ID

    private String name;        //图书名称

    private String author;

    private Category category;    //所属类别

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public String getAuthor() {

        return author;

    }

    public void setAuthor(String author) {

        this.author = author;

    }

    public Category getCategory() {

        return category;

    }

    public void setCategory(Category category) {

        this.category = category;

    }

}

（3）、编写映射文件

(双向)
<hibernate-mapping  package="com.wgh.model">

    <class name="Category" table="tb_Category_manytoone3">

        <id name="id">

            <generator class="native"/>

        </id>

        <property name="name" not-null="true" length="200" />

        <!-- 一对多映射 -->

        <set name="books">

            <key column="categoryId"/>

            <one-to-many class="Book"/>

        </set>

    </class>

</hibernate-mapping>

（单向）
<hibernate-mapping  package="com.wgh.model">

    <class name="Category" table="tb_Category_manytoone0">

        <id name="id">

            <generator class="native"/>

        </id>

        <property name="name" not-null="true" length="200" />

    </class>

</hibernate-mapping>

<hibernate-mapping package="com.wgh.model">

    <class name="Book" table="tb_book_manytoone0">

        <!-- 主键 -->

        <id name="id">

            <generator class="native"/>

        </id>

        <!-- 图书名称 -->

        <property name="name" not-null="true" length="200" />

        <!-- 作者 -->

        <property name="author" not-null="true" length="50"/>

        <!-- 多对一关联映射 -->

        <many-to-one name="category" class="Category">

            <!-- 映射的字段 -->

            <column name="categoryId"/>

        </many-to-one>

    </class>

</hibernate-mapping>

（4）、编写Hibernate的工具类

package com.wgh.hibernate;

import org.hibernate.HibernateException;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

import org.hibernate.service.ServiceRegistryBuilder;

public class HibernateUtil {

    private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();

    private static SessionFactory sessionFactory = null; // SessionFactory对象

    // 静态块

    static {

        try {

            Configuration cfg = new Configuration().configure(); // 加载Hibernate配置文件

            sessionFactory = cfg

                    .buildSessionFactory(new ServiceRegistryBuilder().applySettings(cfg.getProperties())

                            .buildServiceRegistry());

        } catch (Exception e) {

            System.err.println("创建会话工厂失败");

            e.printStackTrace();

        }

    }

    /**

     * 获取Session

     *

     * @return Session

     * @throws HibernateException

     */

    public static Session getSession() throws HibernateException {

        Session session = (Session) threadLocal.get();

        if (session == null || !session.isOpen()) {

            if (sessionFactory == null) {

                rebuildSessionFactory();

            }

            session = (sessionFactory != null) ? sessionFactory.openSession()

                    : null;

            threadLocal.set(session);

        }

        return session;

    }

    /**

     * 重建会话工厂

     */

    public static void rebuildSessionFactory() {

        try {

            Configuration cfg = new Configuration().configure(); // 加载Hibernate配置文件

            sessionFactory = cfg

                    .buildSessionFactory(new ServiceRegistryBuilder().applySettings(cfg.getProperties())

                            .buildServiceRegistry());

        } catch (Exception e) {

            System.err.println("创建会话工厂失败");

            e.printStackTrace();

        }

    }

    /**

     * 获取SessionFactory对象

     *

     * @return SessionFactory对象

     */

    public static SessionFactory getSessionFactory() {

        return sessionFactory;

    }

    /**

     * 关闭Session

     *

     * @throws HibernateException

     */

    public static void closeSession() throws HibernateException {

        Session session = (Session) threadLocal.get();

        threadLocal.set(null);

        if (session != null) {

            session.close(); // 关闭Session

        }

    }

}

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Hibernate一对多单向（双向）关联映射

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