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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

 1 package hibernate.pojo;
 2 
 3 import java.util.Set;
 4 
 5 public class Category {
 6     int id;
 7     String name;
 8 
 9     public int getId() {
10         return id;
11     }
12 
13     public void setId(int id) {
14         this.id = id;
15     }
16 
17     public String getName() {
18         return name;
19     }
20 
21     public void setName(String name) {
22         this.name = name;
23     }
24 
25 }

2.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="hibernate.pojo">
 7     <class name="Category" table="category">
 8         <!-- <cache usage="read-only"/> -->
 9         <id name="id" column="id">
10             <generator class="native">
11             </generator>
12         </id>
13         <property name="name" />
14     </class>
15 </hibernate-mapping>

3.为Product.java增加Category属性

1     Category category;
2     public Category getCategory() {
3         return category;
4     }
5 
6     public void setCategory(Category category) {
7         this.category = category;
8     }

4.在Product.hbm.xml中设置Category多对一关系

 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="hibernate.pojo">
 7     <class name="Product" table="product">
 8         <id name="id" column="id">
 9             <generator class="native">
10             </generator>
11         </id>
12         <property name="name" />
13         <property name="price" />
14         <many-to-one name="category" class="Category" column="cid"></many-to-one>
15     </class>
16      
17 </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

1 <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。

 1 package hibernate.test;
 2 
 3 import java.util.List;
 4 import java.util.Random;
 5 
 6 import org.hibernate.Query;
 7 import org.hibernate.Session;
 8 import org.hibernate.SessionFactory;
 9 import org.hibernate.cfg.Configuration;
10 
11 import hibernate.pojo.Category;
12 import hibernate.pojo.Product;
13 
14 public class testManyToOne {
15 
16     public static void main(String[] args) {
17         // TODO Auto-generated method stub
18 
19         SessionFactory sFactory = new Configuration().configure().buildSessionFactory();
20         Session session = sFactory.openSession();
21         session.beginTransaction();
22 
23         for (int i = 1; i <= 5; i++) {
24             Category category = new Category();
25             category.setName("C" + i);
26             session.save(category);
27         }
28 
29         Query query2 = session.createQuery("from Category");
30         List<Category> categorys = query2.list();
31 
32         for (int i = 1; i <= 10; i++) {
33             Random random = new Random();
34             Product product = (Product) session.get(Product.class, i);
35             product.setCategory(categorys.get(random.nextInt(5)));
36             session.update(product);
37         }
38 
39         session.getTransaction().commit();
40         session.close();
41         sFactory.close();
42     }
43 
44 }

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

 1 package hibernate.pojo;
 2 
 3 import java.util.Set;
 4 
 5 public class Category {
 6     int id;
 7     String name;
 8     Set<Product> products;
 9 
10     public int getId() {
11         return id;
12     }
13 
14     public void setId(int id) {
15         this.id = id;
16     }
17 
18     public String getName() {
19         return name;
20     }
21 
22     public void setName(String name) {
23         this.name = name;
24     }
25 
26     public Set<Product> getProducts() {
27         return products;
28     }
29 
30     public void setProducts(Set<Product> products) {
31         this.products = products;
32     }
33 
34 }

2.为Category.hbm.xml增加one-to-many映射

 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="hibernate.pojo">
 7     <class name="Category" table="category">
 8         <!-- <cache usage="read-only"/> -->
 9         <id name="id" column="id">
10             <generator class="native">
11             </generator>
12         </id>
13         <property name="name" />
14         <set name="products" lazy="true">
15             <key column="cid" not-null="false"></key>
16             <one-to-many class="Product" />
17         </set>
18     </class>
19 
20 </hibernate-mapping>

3.测试

 1 package hibernate.test;
 2 
 3 import java.util.List;
 4 
 5 import org.hibernate.Query;
 6 import org.hibernate.Session;
 7 import org.hibernate.SessionFactory;
 8 import org.hibernate.cfg.Configuration;
 9 
10 import hibernate.pojo.Category;
11 import hibernate.pojo.Product;
12 
13 public class testOneToMany {
14 
15     public static void main(String[] args) {
16         // TODO Auto-generated method stub
17 
18         SessionFactory sFactory = new Configuration().configure().buildSessionFactory();
19         Session session = sFactory.openSession();
20         session.beginTransaction();
21 
22         Query query = session.createQuery("from Category");
23         List<Category> categories = query.list();
24         for (Category c : categories) {
25             System.out.println("属于" + c.getName() + "类的商品有：");
26             for (Product p : c.getProducts()) {
27                 System.out.println(p.getName());
28             }
29         }
30 
31         session.getTransaction().commit();
32         session.close();
33         sFactory.close();
34     }
35 
36 }

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

 1 package hibernate.pojo;
 2 
 3 import java.util.Set;
 4 
 5 public class User {
 6     int id;
 7     String name;
 8     Set<Product> products;
 9 
10     public int getId() {
11         return id;
12     }
13 
14     public void setId(int id) {
15         this.id = id;
16     }
17 
18     public String getName() {
19         return name;
20     }
21 
22     public void setName(String name) {
23         this.name = name;
24     }
25 
26     public Set<Product> getProducts() {
27         return products;
28     }
29 
30     public void setProducts(Set<Product> products) {
31         this.products = products;
32     }
33 
34 }

2.User.hbm.xml

 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="hibernate.pojo">
 7     <class name="User" table="user">
 8         <id name="id" column="id">
 9             <generator class="native">
10             </generator>
11         </id>
12         <property name="name" />
13 
14         <set name="products" table="user_product" lazy="false">
15             <key column="uid" />
16             <many-to-many column="pid" class="Product" />
17         </set>
18 
19     </class>
20 
21 </hibernate-mapping>

3.Product.java

1     Set<User> users;    
2     public Set<User> getUsers() {
3         return users;
4     }
5 
6     public void setUsers(Set<User> users) {
7         this.users = users;
8     }

4.Product.hbm.xml

 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="hibernate.pojo">
 7     <class name="Product" table="product">
 8         <id name="id" column="id">
 9             <generator class="native">
10             </generator>
11         </id>
12         <!--version元素必须紧挨着id后面  -->
13         <version name="version" column="ver" type="int"></version>
14         <property name="name" />
15         <property name="price" />
16         <many-to-one name="category" class="Category" column="cid"></many-to-one>
17         <set name="users" table="user_product" lazy="false" >
18             <key column="pid"></key>
19             <many-to-many column="uid" class="User"></many-to-many>
20         </set>
21     </class>
22      
23 </hibernate-mapping>

5.在hibernate中增加User的映射

1 <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。

 1 package hibernate.test;
 2 
 3 import java.util.HashSet;
 4 import java.util.List;
 5 import java.util.Set;
 6 
 7 import org.hibernate.Query;
 8 import org.hibernate.Session;
 9 import org.hibernate.SessionFactory;
10 import org.hibernate.cfg.Configuration;
11 
12 import hibernate.pojo.Product;
13 import hibernate.pojo.User;
14 
15 public class testManyToMany {
16 
17     public static void main(String[] args) {
18         // TODO Auto-generated method stub
19 
20         SessionFactory sFactory = new Configuration().configure().buildSessionFactory();
21         Session session = sFactory.openSession();
22         session.beginTransaction();
23         // 添加三个用户
24         Set<User> users = new HashSet<User>();
25         for (int i = 0; i < 3; i++) {
26             User user = new User();
27             user.setName("user" + i);
28             users.add(user);
29             session.save(user);
30         }
31         // 一件商品多个人购买
32         Product p1 = (Product) session.get(Product.class, 2);
33         p1.setUsers(users);
34         session.save(p1);
35 
36         // 一个人购买多个商品
37         // 获取商品列表
38 
39         User user = new User();
40         user.setName("user3");
41         session.save(user);
42 
43         Query query = session.createQuery("from Product");
44         List<Product> products = query.list();
45         Set<Product> products2 = new HashSet<Product>();
46         for (int i = 0; i < products.size(); i++) {
47             products2.add(products.get(i));
48         }
49         User u1 = (User) session.get(User.class, 4);
50         u1.setProducts(products2);
51         session.save(u1);
52 
53         session.getTransaction().commit();
54         session.close();
55         sFactory.close();
56     }
57 
58 }

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原文地址：https://www.cnblogs.com/lyj-gyq/p/9188565.html