Hibernate一对多关系详解

一方：

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.entity.Author" table="Author" >        <id name="id" type="java.lang.Integer">            <column name="id" />            <generator class="native" />        </id>        <property name="name" type="java.lang.String">            <column name="name" length="50" not-null="true" />        </property>        <set name="books" inverse="true" cascade="save-update">            <key column="author_id"/>            <one-to-many class="com.entity.Book"/>        </set>    </class></hibernate-mapping>

多方：

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.entity.Book" table="Book" >        <id name="id" type="java.lang.Integer">            <column name="id" />            <generator class="native" />        </id>        <property name="name" type="java.lang.String">            <column name="name" length="50" not-null="true" />        </property>        <many-to-one name="author" class="com.entity.Author" cascade="save-update">        <column name="author_id"></column>        </many-to-one>    </class></hibernate-mapping>

Insert操作：

从一方操作：

public void insert(){Transaction transaction = null;try {transaction = session.beginTransaction();Author author = new Author();author.setName("李威");Book book = new Book();book.setName("斗罗大陆");book.setAuthor(author);author.getBooks().add(book);session.save(author);transaction.commit();} catch (HibernateException e) {// TODO: handle exceptione.printStackTrace();if(transaction!=null){transaction.rollback();}}}

从多方操作：

public void insert(){Transaction transaction = null;try {transaction = session.beginTransaction();Author author = new Author();author.setName("李威");Book book = new Book();book.setName("斗罗大陆");book.setAuthor(author);author.getBooks().add(book);session.save(author);transaction.commit();} catch (HibernateException e) {// TODO: handle exceptione.printStackTrace();if(transaction!=null){transaction.rollback();}}}

明显从一方操作需要建立更复杂的联系，所以，应该从多方建立联系。

更新操作：

一方：

public void modify(){Transaction transaction = null;try {transaction = session.beginTransaction();Book book = (Book)session.load(Book.class, 18);Author author = (Author)session.load(Author.class, 23);book.setAuthor(author);session.update(book);transaction.commit();} catch (HibernateException e) {// TODO: handle exceptione.printStackTrace();if(transaction!=null){transaction.rollback();}}}

多方：

public void modify(){Transaction transaction = null;try {transaction = session.beginTransaction();Book book = (Book)session.load(Book.class, 18);Author author = (Author)session.load(Author.class, 24);book.setAuthor(author);author.getBooks().add(book);session.update(author);transaction.commit();} catch (HibernateException e) {// TODO: handle exceptione.printStackTrace();if(transaction!=null){transaction.rollback();}}}

查询操作 ：

一方：注意此时如果没有设置懒加载，获取的set是代理对象，如果session关闭后，在获取对象属性，会遇到懒加载问题，可通过设置lazy=”false”,或者设置session在获取属性后关闭解决。

public void select(){Transaction transaction = null;Set<Book> books = null;try {transaction = session.beginTransaction();Author author = (Author)session.load(Author.class, 23);books = author.getBooks();for (Book book : books) {System.out.println(book.getName());}transaction.commit();} catch (HibernateException e) {// TODO: handle exceptione.printStackTrace();if(transaction!=null){transaction.rollback();}}}

多方：同样存在懒加载问题

public void select(){Transaction transaction = null;Author author = null;try {transaction = session.beginTransaction();Book book = (Book)session.load(Book.class, 16);author = book.getAuthor();System.out.println(author.getName());transaction.commit();} catch (HibernateException e) {// TODO: handle exceptione.printStackTrace();if(transaction!=null){transaction.rollback();}

删除操作：

一方：如果需要级联删除多方，将cascade设置为all

public void delete(){Transaction transaction = null;try {transaction = session.beginTransaction();//Book book = (Book)session.load(Book.class, 18);Author author = (Author)session.load(Author.class, 23);session.delete(author);transaction.commit();} catch (HibernateException e) {// TODO: handle exceptione.printStackTrace();if(transaction!=null){transaction.rollback();}}}

多方：

public void delete(){Transaction transaction = null;try {transaction = session.beginTransaction();Book book = (Book)session.load(Book.class, 18);//Author author = (Author)session.load(Author.class, 23);session.delete(book);transaction.commit();} catch (HibernateException e) {// TODO: handle exceptione.printStackTrace();if(transaction!=null){transaction.rollback();}}}