392、Java框架47 -【Hibernate - 关系 - 实现多对一】 2020.10.20

0、目录

1、关系：多对一2、效果3、准备Category.java4、准备Category.hbm.xml5、为Product.java增加Category属性6、在Product.hbm.xml中设置Category 多对一关系7、在hibernate.cfg.xml中增加Category的映射8、TestHibernate 测试many-to-one关系8、参考链接

1、关系：多对一

一个Product对应一个Category 一个Category对应多个Product

所以Product和Category是多对一的关系 本例讲解如何使用Hibernate实现多对一关系

2、效果

通过多对一关系，设置了id=8的产品对应 id=1的分类

3、准备Category.java

package com.how2java.pojo; public class Category { public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } int id; String name; }

4、准备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.how2java.pojo"> <class name="Category" table="category_"> <id name="id" column="id"> <generator class="native"> </generator> </id> <property name="name" /> </class> </hibernate-mapping>

5、为Product.java增加Category属性

package com.how2java.pojo; public class Product { int id; String name; float price; Category category; public Category getCategory() { return category; } public void setCategory(Category category) { this.category = category; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public float getPrice() { return price; } public void setPrice(float price) { this.price = price; } }

6、在Product.hbm.xml中设置Category 多对一关系

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

使用many-to-one 标签设置多对一关系 name=“category” 对应Product类中的category属性 class=“Category” 表示对应Category类 column=“cid” 表示指向 category_表的外键

<?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.how2java.pojo"> <class name="Product" table="product_"> <id name="id" column="id"> <generator class="native"> </generator> </id> <property name="name" /> <property name="price" /> <many-to-one name="category" class="Category" column="cid" /> </class> </hibernate-mapping>

7、在hibernate.cfg.xml中增加Category的映射

新增Category映射

<?xml version='1.0' encoding='utf-8'?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <!-- Database connection settings --> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="connection.url">jdbc:mysql://localhost:3306/test?characterEncoding=GBK</property> <property name="connection.username">root</property> <property name="connection.password">admin</property> <!-- SQL dialect --> <property name="dialect">org.hibernate.dialect.MySQLDialect</property> <property name="current_session_context_class">thread</property> <property name="show_sql">true</property> <property name="hbm2ddl.auto">update</property> <mapping resource="com/how2java/pojo/Product.hbm.xml" /> <mapping resource="com/how2java/pojo/Category.hbm.xml" /> </session-factory> </hibernate-configuration>

8、TestHibernate 测试many-to-one关系

在这个测试例子中，增加了一个新的Category对象"c1" 并将其设置为id=8的product的category

package com.how2java.test; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.cfg.Configuration; import com.how2java.pojo.Category; import com.how2java.pojo.Product; public class TestHibernate { public static void main(String[] args) { SessionFactory sf = new Configuration().configure().buildSessionFactory(); Session s = sf.openSession(); s.beginTransaction(); Category c =new Category(); c.setName("c1"); s.save(c); Product p = (Product) s.get(Product.class, 8); p.setCategory(c); s.update(p); s.getTransaction().commit(); s.close(); sf.close(); } }

8、参考链接

[01] How2j - Hibernate - 关系 - 实现多对一