hibernate 多对一双向映射关系

最新推荐文章于 2024-07-24 10:59:17 发布

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本文介绍了一个关于图书和图书类别类的设计，包括Book类和Category类，并详细展示了这两个类之间的多对一和一对多的关系映射，同时提供了Hibernate配置文件的具体实现。

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Book类(图书类)：

package com.hc.model;

public class Book {
	private Integer id;			
	private String name;		
	private String author;		
	private Category category;	
	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;
	}
}

Category类(图书类别类，多本图书对应一种类别)：

package com.hc.model;

public class Category {
	private Integer id;			
	private String name;		
	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;
	}
}

Book表：

Category表：

Book映射文件(Book.hbm.xml)：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hc.model">
	<class name="Book" table="book_manytoone">
		<!-- 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" cascade="save-update">
			<!-- 映射的字段 -->
			<column name="categoryId"/>
		</many-to-one>
	</class>
</hibernate-mapping>

Category映射文件(Category.hbm.xml):

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping  package="com.wgh.model">
	<class name="Category" table="tb_Category_manytoone">
		<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>

测试：

Session session = null;			//声明Session对象
		try {
			//获取Session
			session = HibernateUtil.getSession();
			//开启事务
			session.beginTransaction();
			System.out.println("*********查询图书对象************");
			//查询图书对象
			Book book1 = (Book)session.get(Book.class, new Integer(1));
			System.out.println("图书名称：" + book1.getName());
			System.out.println("图书类别：" + book1.getCategory().getName());
			System.out.println("*********查询类别对象************");
			//查询类别对象
			Category c = (Category) session.load(Category.class, new Integer(1));
			System.out.println("类别名称：" + c.getName());
			Set<Book> books = c.getBooks();		//获取类别中的所有图书
			//通过迭代输出图书名称
			for (Iterator<Book> it = books.iterator(); it.hasNext();) {
				Book book2 = (Book) it.next();
				System.out.println("图书名称：" + book2.getName());
			}
			//提交事务
			session.getTransaction().commit();
		} catch (Exception e) {
			e.printStackTrace();
			//出错将回滚事务
			session.getTransaction().rollback();
		}finally{
			//关闭Session对象
			HibernateUtil.closeSession();
		}