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
第一步 准备Category.java
1 package com.ghw.pojo; 2 ??3 public class Category { 4 ??5 ????public int getId() { 6 ????????return id; 7 ????} 8 ????public void setId(int id) { 9 ????????this.id = id;10 ????}11 ????public String getName() {12 ????????return name;13 ????}14 ????public void setName(String name) {15 ????????this.name = name;16 ????}17 ????int id;18 ????String name;19 }第二步 准备Category.hbm.xml
1 <?xml version="1.0"?> 2 ??3 <!DOCTYPE hibernate-mapping PUBLIC 4 ????????"-//Hibernate/Hibernate Mapping DTD 3.0//EN" 5 ????????"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 6 <hibernate-mapping package="com.ghw.pojo"> 7 ????<class name="Category" table="category_"> ???8 ????????<id name="id" column="id"> 9 ????????????<generator class="native">10 ????????????</generator>11 ????????</id>12 ????????<property name="name" />13 ????</class> ?14 </hibernate-mapping>
第三步 在Product.java中添加Category属性和它的setter和getter方法
1 package com.ghw.pojo; 2 public class Product { 3 ????private int id; 4 ????private String name; 5 ????private float price; 6 ????private Category category; 7 ????public Category getCategory() { 8 ????????return category; 9 ????}10 ????public void setCategory(Category category) {11 ????????this.category = category;12 ????}13 ????public int getId() {14 ????????return id;15 ????}16 ????public void setId(int id) {17 ????????this.id = id;18 ????}19 ????public String getName() {20 ????????return name;21 ????}22 ????public void setName(String name) {23 ????????this.name = name;24 ????}25 ????public float getPrice() {26 ????????return price;27 ????}28 ????public void setPrice(float price) {29 ????????this.price = price;30 ????} 31 }第四步 在Hibernate.hbm.xml文件中添加Category.hbm.xml的mappering映射
新增Category映射
1 <?xml version=‘1.0‘ encoding=‘utf-8‘?> 2 <!DOCTYPE hibernate-configuration PUBLIC 3 ???????"-//Hibernate/Hibernate Configuration DTD 3.0//EN" 4 "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> 5 <hibernate-configuration> 6 ??7 ????<session-factory> 8 ????????<!-- Database connection settings --> 9 ????????<property name="connection.driver_class">com.mysql.jdbc.Driver</property>10 ????????<property name="connection.url">jdbc:mysql://localhost:3306/test?characterEncoding=GBK</property>11 ????????<property name="connection.username">root</property>12 ????????<property name="connection.password">admin</property>13 ????????<!-- SQL dialect -->14 ????????<property name="dialect">org.hibernate.dialect.MySQLDialect</property>15 ????????<property name="current_session_context_class">thread</property>16 ????????<property name="show_sql">true</property>17 ????????<property name="hbm2ddl.auto">update</property>18 ????????<mapping resource="com/ghw/pojo/Product.hbm.xml" />19 ????????<mapping resource="com/ghw/pojo/Category.hbm.xml" />20 ????</session-factory>21 ?22 </hibernate-configuration>
第五步 在Product.hbm.xml中设置Category 多对一关系
many-to-one中
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
1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC 3 ????????"-//Hibernate/Hibernate Mapping DTD 3.0//EN" 4 ????????"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 5 ??6 <hibernate-mapping package="com.ghw.pojo"> 7 ????<class name="Product" table="product_"> 8 ????????<id name="id" column="id"> 9 ????????????<generator class="native">10 ????????????</generator>11 ????????</id>12 ?13 ????????<property name="name" />14 ????????<property name="price" />15 ????????<many-to-one name="category" class="Category" column="cid" />16 ????</class>17 ?????18 </hibernate-mapping>
第六步 TestHibernate 测试many-to-one关系
一定要先保存c再保存p，否则报错抛出异常。
1 package com.how2java.test; 2 ???3 import org.hibernate.Session; 4 import org.hibernate.SessionFactory; 5 import org.hibernate.cfg.Configuration; 6 ??7 import com.ghw.pojo.Category; 8 import com.ghw.pojo.Product; 9 ?10 public class TestHibernate {11 ????public static void main(String[] args) {12 ????????SessionFactory sf = new Configuration().configure().buildSessionFactory();13 ??14 ????????Session s = sf.openSession();15 ????????s.beginTransaction();16 ?????????17 ????????Category c =new Category();18 ????????c.setName("c1");19 ????????s.save(c);20 ?????????21 ????????Product p = (Product) s.get(Product.class, 8);22 ????????p.setCategory(c);23 ????????s.update(p);24 ?????????25 ????????s.getTransaction().commit();26 ????????s.close();27 ????????sf.close();28 ????}29 }HIBERNATE 实现多对一
原文地址：https://www.cnblogs.com/nuanbear/p/8602354.html