Hibernate O/R 映射

一、多對一

　　一個Product對應一個Category，一個Category對應多個Product，所以Product和Category是多對一的關系。使用hibernate實現多對一。

1.準備Category類

 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.準備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.為Product.java增加Category屬性

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中設置Category多對一關系

 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 標簽設置多對一關系
name="category" 對應Product類中的category屬性
class="Category" 表示對應Category類
column="cid" 表示指向 category_表的外鍵

5.在hibernate.cfg.xml中增加Category的映射

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

6.測試

二、一對多

三、多對多

筆記45 Hibernate快速入門（二）