笔记45 Hibernate快速入门（二）

Hibernate O/R 映射

一、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。使用hibernate实现多对一。

1.准备Category类

 package hibernate.pojo;

 import java.util.Set;

 public class Category {
     int id;
     String name;

     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;
     }

 }

2.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="hibernate.pojo">
     <class name="Category" table="category">
         <!-- <cache usage="read-only"/> -->
         <id name="id" column="id">
             <generator class="native">
             </generator>
         </id>
         <property name="name" />
     </class>
 </hibernate-mapping>

3.为Product.java增加Category属性

     Category category;
     public Category getCategory() {
         return category;
     }

     public void setCategory(Category category) {
         this.category = category;
     } 

4.在Product.hbm.xml中设置Category多对一关系

 <?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="hibernate.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"></many-to-one>
     </class>

 </hibernate-mapping>

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

5.在hibernate.cfg.xml中增加Category的映射

 <mapping resource="hibernate/pojo/Category.hbm.xml" />

6.测试

　　在这个测试例子中，增加了五个新的Category对象，然后对商品进行随机分类。

 package hibernate.test;

 import java.util.List;
 import java.util.Random;

 import org.hibernate.Query;
 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 import org.hibernate.cfg.Configuration;

 import hibernate.pojo.Category;
 import hibernate.pojo.Product;

 public class testManyToOne {

     public static void main(String[] args) {
         // TODO Auto-generated method stub

         SessionFactory sFactory = new Configuration().configure().buildSessionFactory();
         Session session = sFactory.openSession();
         session.beginTransaction();

         for (int i = 1; i <= 5; i++) {
             Category category = new Category();
             category.setName("C" + i);
             session.save(category);
         }

         Query query2 = session.createQuery("from Category");
         List<Category> categorys = query2.list();

         for (int i = 1; i <= 10; i++) {
             Random random = new Random();
             Product product = (Product) session.get(Product.class, i);
             product.setCategory(categorys.get(random.nextInt(5)));
             session.update(product);
         }

         session.getTransaction().commit();
         session.close();
         sFactory.close();
     }

 }

二、一对多

　　一个Product对应一个Category，一个Category对应多个Product，所以Category和Product是一对多的关系。

1.为Category增加一个Set集合

 package hibernate.pojo;

 import java.util.Set;

 public class Category {
     int id;
     String name;
     Set<Product> products;

     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 Set<Product> getProducts() {
         return products;
     }

     public void setProducts(Set<Product> products) {
         this.products = products;
     }

 }

2.为Category.hbm.xml增加one-to-many映射

 <?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="hibernate.pojo">
     <class name="Category" table="category">
         <!-- <cache usage="read-only"/> -->
         <id name="id" column="id">
             <generator class="native">
             </generator>
         </id>
         <property name="name" />
         <set name="products" lazy="true">
             <key column="cid" not-null="false"></key>
             <one-to-many class="Product" />
         </set>
     </class>

 </hibernate-mapping>

3.测试

 package hibernate.test;

 import java.util.List;

 import org.hibernate.Query;
 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 import org.hibernate.cfg.Configuration;

 import hibernate.pojo.Category;
 import hibernate.pojo.Product;

 public class testOneToMany {

     public static void main(String[] args) {
         // TODO Auto-generated method stub

         SessionFactory sFactory = new Configuration().configure().buildSessionFactory();
         Session session = sFactory.openSession();
         session.beginTransaction();

         Query query = session.createQuery("from Category");
         List<Category> categories = query.list();
         for (Category c : categories) {
             System.out.println("属于" + c.getName() + "类的商品有：");
             for (Product p : c.getProducts()) {
                 System.out.println(p.getName());
             }
         }

         session.getTransaction().commit();
         session.close();
         sFactory.close();
     }

 }

三、多对多

　　一种Product可以被多个User购买 一个User可以购买多种Product 所以Product和User之间的关系是多对多 many-to-many 要实现多对多关系，必须有一张中间表 user_product 用于维护 User和Product之间的关系。

1.User.java

 package hibernate.pojo;

 import java.util.Set;

 public class User {
     int id;
     String name;
     Set<Product> products;

     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 Set<Product> getProducts() {
         return products;
     }

     public void setProducts(Set<Product> products) {
         this.products = products;
     }

 }

2.User.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="hibernate.pojo">
     <class name="User" table="user">
         <id name="id" column="id">
             <generator class="native">
             </generator>
         </id>
         <property name="name" />

         <set name="products" table="user_product" lazy="false">
             <key column="uid" />
             <many-to-many column="pid" class="Product" />
         </set>

     </class>

 </hibernate-mapping>

3.Product.java

     Set<User> users;
     public Set<User> getUsers() {
         return users;
     }

     public void setUsers(Set<User> users) {
         this.users = users;
     }

4.Product.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="hibernate.pojo">
     <class name="Product" table="product">
         <id name="id" column="id">
             <generator class="native">
             </generator>
         </id>
         <!--version元素必须紧挨着id后面  -->
         <version name="version" column="ver" type="int"></version>
         <property name="name" />
         <property name="price" />
         <many-to-one name="category" class="Category" column="cid"></many-to-one>
         <set name="users" table="user_product" lazy="false" >
             <key column="pid"></key>
             <many-to-many column="uid" class="User"></many-to-many>
         </set>
     </class>

 </hibernate-mapping>

5.在hibernate中增加User的映射

 <mapping resource="hibernate/pojo/User.hbm.xml" />

6.测试

首先添加三个用户，然后实现一件商品多人购买和一个人购买多件商品（再新增用户“user3”）两个功能。

 package hibernate.test;

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

 import org.hibernate.Query;
 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 import org.hibernate.cfg.Configuration;

 import hibernate.pojo.Product;
 import hibernate.pojo.User;

 public class testManyToMany {

     public static void main(String[] args) {
         // TODO Auto-generated method stub

         SessionFactory sFactory = new Configuration().configure().buildSessionFactory();
         Session session = sFactory.openSession();
         session.beginTransaction();
         // 添加三个用户
         Set<User> users = new HashSet<User>();
         for (int i = 0; i < 3; i++) {
             User user = new User();
             user.setName("user" + i);
             users.add(user);
             session.save(user);
         }
         // 一件商品多个人购买
         Product p1 = (Product) session.get(Product.class, 2);
         p1.setUsers(users);
         session.save(p1);

         // 一个人购买多个商品
         // 获取商品列表

         User user = new User();
         user.setName("user3");
         session.save(user);

         Query query = session.createQuery("from Product");
         List<Product> products = query.list();
         Set<Product> products2 = new HashSet<Product>();
         for (int i = 0; i < products.size(); i++) {
             products2.add(products.get(i));
         }
         User u1 = (User) session.get(User.class, 4);
         u1.setProducts(products2);
         session.save(u1);

         session.getTransaction().commit();
         session.close();
         sFactory.close();
     }

 }