Hibernate关系映射1：单向N-1关联

Hibernate关系映射1：单向N-1关联

单向N-1关联

---

单向N-1关系，比如多个人对应一个地址，只需从人实体端可以找到对应的地址实体，无须关系某个地址的全部住户。

单向 n-1 关联只需从 n 的一端可以访问 1 的一端。

域模型

从 Book到 Book_Category的多对一单向关联需要在Book类中定义一个 Book_Category属性, 而在 Book_Category类中无需定义存放 Book对象的集合属性

                                    

关系数据模型

Demo

Hibernate 使用 元素来映射多对一关联关系<many-to-one name="customer" class="Customer" column="CUSTOMER_ID" cascade="all" />

• name: 设定待映射的持久化类的属性的名字
• column: 设定和持久化类的属性对应的表的外键
• class：设定待映射的持久化类的属性的类型
• cascade：意味着系统将先自动级联插入主表记录，也就是说先持久化Customer对象，再持久化Person对象。开发时不建议使用该属性，建议使用手工的方式。

数据库代码：

下面是实体对象，分为Book（书本）和Book_Category（书本类别）,其中书本和书本类别是N-1关系。

Book实体类：

package com.liuyongqi.MavenHibernateDemo3.entity;
/**
 * 书本实体类
 * @author Administrator
 * @data   2018年8月2日
 * @time   下午7:43:54
 */

import java.util.Date;

public class Book {
	
	private Integer book_id ;
	private String book_name ;
	private Float book_price ;
	private String book_auther ;
	private Date book_date ;
	private Book_Category book_category;
	
	public Book() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Book(String book_name, Float book_price, String book_auther, Date book_date) {
		super();
		this.book_name = book_name;
		this.book_price = book_price;
		this.book_auther = book_auther;
		this.book_date = book_date;
	}
	public Book(Integer book_id, String book_name, Float book_price, String book_auther, Date book_date,
			Book_Category book_category) {
		super();
		this.book_id = book_id;
		this.book_name = book_name;
		this.book_price = book_price;
		this.book_auther = book_auther;
		this.book_date = book_date;
		this.book_category = book_category;
	}
	public Integer getBook_id() {
		return book_id;
	}
	public void setBook_id(Integer book_id) {
		this.book_id = book_id;
	}
	public String getBook_name() {
		return book_name;
	}
	public void setBook_name(String book_name) {
		this.book_name = book_name;
	}
	public Float getBook_price() {
		return book_price;
	}
	public void setBook_price(Float book_price) {
		this.book_price = book_price;
	}
	public String getBook_auther() {
		return book_auther;
	}
	public void setBook_auther(String book_auther) {
		this.book_auther = book_auther;
	}
	public Date getBook_date() {
		return book_date;
	}
	public void setBook_date(Date book_date) {
		this.book_date = book_date;
	}
	public Book_Category getBook_category() {
		return book_category;
	}
	public void setBook_category(Book_Category book_category) {
		this.book_category = book_category;
	}
	@Override
	public String toString() {
		return "Book [book_id=" + book_id + ", book_name=" + book_name + ", book_price=" + book_price + ", book_auther="
				+ book_auther + ", book_date=" + book_date + ", book_category=" + book_category + "]";
	}	
	
	

}

Book_Category实体类：

package com.liuyongqi.MavenHibernateDemo3.entity;

import java.util.HashSet;
import java.util.Set;

/**
 * 书本类别实体类
 * @author Administrator
 * @data   2018年8月2日
 * @time   下午7:46:08
 */
public class Book_Category {
	private Integer book_category_id;
	private String book_category_name;
	
	public Book_Category() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Book_Category(String book_category_name) {
		super();
		this.book_category_name = book_category_name;
	}
	public Book_Category(Integer book_category_id, String book_category_name) {
		super();
		this.book_category_id = book_category_id;
		this.book_category_name = book_category_name;
	}
	public Integer getBook_category_id() {
		return book_category_id;
	}
	public void setBook_category_id(Integer book_category_id) {
		this.book_category_id = book_category_id;
	}
	public String getBook_category_name() {
		return book_category_name;
	}
	public void setBook_category_name(String book_category_name) {
		this.book_category_name = book_category_name;
	}
	@Override
	public String toString() {
		return "Book_Category [book_category_id=" + book_category_id + ", book_category_name=" + book_category_name
				+ "]";
	}
	
	

}

Book_Category实体类映射文件Book_Category.hbm.xml：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2018-8-4 9:12:09 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="com.liuyongqi.MavenHibernateDemo3.entity.Book_Category" table="book_category">
        <id name="book_category_id" type="java.lang.Integer">
            <column name="book_category_id" />
            <generator class="native" />
        </id>
        <property name="book_category_name" type="java.lang.String">
            <column name="book_category_name" />
        </property>
    </class>
</hibernate-mapping>

Book实体类映射文件Book.hbm.xml：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2018-8-4 9:12:09 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="com.liuyongqi.MavenHibernateDemo3.entity.Book" table="book">
        <id name="book_id" type="java.lang.Integer">
            <column name="book_id" />
            <generator class="native" />
        </id>
        <property name="book_name" type="java.lang.String">
            <column name="book_name" />
        </property>
        <property name="book_price" type="java.lang.Float">
            <column name="book_price" />
        </property>
        <property name="book_auther" type="java.lang.String">
            <column name="book_auther" />
        </property>
        <property name="book_date" type="java.util.Date">
            <column name="book_date" />
        </property>
        <many-to-one name="book_category" class="com.liuyongqi.MavenHibernateDemo3.entity.Book_Category" fetch="join" cascade="all">
            <column name="book_category_id" />
        </many-to-one>
    </class>
</hibernate-mapping>

测试类：

package com.liuyongqi.MavenHibernateDemo3.test;

import java.util.Date;

import org.hibernate.Session;
import org.hibernate.Transaction;

import com.liuyongqi.MavenHibernateDemo3.entity.Book;
import com.liuyongqi.MavenHibernateDemo3.entity.Book_Category;
import com.liuyongqi.MavenHibernateDemo3.util.SessionFactoryUtil;

/**
 * 测试类
 * @author Administrator
 * @data   2018年8月2日
 * @time   下午8:13:18
 */
public class Test {
	public static void main(String[] args) {
		Session session = SessionFactoryUtil.openSession();
		Transaction transaction = session.beginTransaction();
		Book_Category book_category=new Book_Category();
		book_category.setBook_category_name("文学");
		Book_Category book_category1=new Book_Category();
		book_category1.setBook_category_name("科幻");
		Book_Category book_category2=new Book_Category();
		book_category2.setBook_category_name("历史");
		Book_Category book_category3=new Book_Category();
		book_category3.setBook_category_name("言情");
		Book_Category book_category4=new Book_Category();
		book_category4.setBook_category_name("漫画");
		Book_Category book_category5=new Book_Category();
		book_category5.setBook_category_name("悬疑");
		Book book=new Book();
		book.setBook_name("读者");
		book.setBook_price(21.5F);
		book.setBook_auther("读者出版传媒有限公司");;
		book.setBook_date(new Date());
		book.setBook_category(book_category);
		Book book1=new Book();
		book1.setBook_name("蓝血人");
		book1.setBook_price(50F);
		book1.setBook_auther("卫斯理");
		book1.setBook_date(new Date());
		book1.setBook_category(book_category1);
		Book book2=new Book();
		book2.setBook_name("傲慢与偏见");
		book2.setBook_price(80F);
		book2.setBook_auther("简.奥斯丁");
		book2.setBook_date(new Date());
		book2.setBook_category(book_category3);
		Book book3=new Book();
		book3.setBook_name("中国历史");
		book3.setBook_price(21.5F);
		book3.setBook_auther("人民");
		book3.setBook_date(new Date());
		book3.setBook_category(book_category2);
		Book book4=new Book();
		book4.setBook_name("七龙珠");
		book4.setBook_price(21.5F);
		book4.setBook_auther("不知道");
		book4.setBook_date(new Date());
		book4.setBook_category(book_category4);
		Book book5=new Book();
		book5.setBook_name("名侦探柯南");
		book5.setBook_price(50F);
		book5.setBook_auther("宫崎骏");
		book5.setBook_date(new Date());
		book5.setBook_category(book_category5);
		
		session.save(book);
		session.save(book1);
		session.save(book2);
		session.save(book3);
		session.save(book4);
		session.save(book5);
		
		transaction.commit();
		
		SessionFactoryUtil.closeSession();
		
	}

}

由于在Order.hbm.xml中配置了cascade="all"，所以只需要保存order对象即可，会首先自动保存级联的Customer对象。

运行后的结果：

控制台结果：

Hibernate: 
    insert 
    into
        book_category
        (book_category_name) 
    values
        (?)
Hibernate: 
    insert 
    into
        book
        (book_name, book_price, book_auther, book_date, book_category_id) 
    values
        (?, ?, ?, ?, ?)
Hibernate: 
    insert 
    into
        book_category
        (book_category_name) 
    values
        (?)
Hibernate: 
    insert 
    into
        book
        (book_name, book_price, book_auther, book_date, book_category_id) 
    values
        (?, ?, ?, ?, ?)
Hibernate: 
    insert 
    into
        book_category
        (book_category_name) 
    values
        (?)
Hibernate: 
    insert 
    into
        book
        (book_name, book_price, book_auther, book_date, book_category_id) 
    values
        (?, ?, ?, ?, ?)
Hibernate: 
    insert 
    into
        book_category
        (book_category_name) 
    values
        (?)
Hibernate: 
    insert 
    into
        book
        (book_name, book_price, book_auther, book_date, book_category_id) 
    values
        (?, ?, ?, ?, ?)
Hibernate: 
    insert 
    into
        book_category
        (book_category_name) 
    values
        (?)
Hibernate: 
    insert 
    into
        book
        (book_name, book_price, book_auther, book_date, book_category_id) 
    values
        (?, ?, ?, ?, ?)
Hibernate: 
    insert 
    into
        book_category
        (book_category_name) 
    values
        (?)
Hibernate: 
    insert 
    into
        book
        (book_name, book_price, book_auther, book_date, book_category_id) 
    values
        (?, ?, ?, ?, ?)

希望大家自己测试一下，才能自己真正的掌握。

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