hibernate映射-双向n-n关联关系

（学习记录，错误不足之处，请您耐心指正^_^）

hibernate映射-双向n-n关联关系

一、代码示例：

{类文件↓}

Category.class

package com.zit.hibernate.n2n.both;

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

public class Category {
    
    private Integer id;
    private String name;
    
    private Set<Item> items = new HashSet<>();
    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Set<Item> getItems() {
        return items;
    }
    public void setItems(Set<Item> items) {
        this.items = items;
    }
    
}

Category.class

Item.class

 1 package com.zit.hibernate.n2n.both;
 2 
 3 import java.util.HashSet;
 4 import java.util.Set;
 5 
 6 public class Item {
 7     
 8     private Integer id;
 9     private String name;
10     
11     private Set<Category> categories = new HashSet<>();
12 
13     
14     public Set<Category> getCategories() {
15         return categories;
16     }
17     public void setCategories(Set<Category> categories) {
18         this.categories = categories;
19     }
20     public Integer getId() {
21         return id;
22     }
23     public void setId(Integer id) {
24         this.id = id;
25     }
26     public String getName() {
27         return name;
28     }
29     public void setName(String name) {
30         this.name = name;
31     }
32     
33 }

Item.class

{映射文件↓}

Category.hbm.xml

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2015-12-25 13:55:35 by Hibernate Tools 3.4.0.CR1 -->
 5 <hibernate-mapping package="com.zit.hibernate.n2n.both">
 6     <class name="Category" table="CATEGORIES">
 7         <id name="id" type="java.lang.Integer">
 8             <column name="ID" />
 9             <generator class="native" />
10         </id>
11         <property name="name" type="java.lang.String">
12             <column name="NAME" />
13         </property>
14         <set name="items" table="CATEGORIES_ITEMS">
15             <key>
16                 <column name="C_ID" />
17             </key>
18             <many-to-many class="Item" column="I_ID">
19             </many-to-many>
20         </set>
21     </class>
22 </hibernate-mapping>

Category.hbm.xml

Item.hbm.xml

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2015-12-25 13:55:35 by Hibernate Tools 3.4.0.CR1 -->
 5 <hibernate-mapping package="com.zit.hibernate.n2n.both">
 6     <class name="Item" table="ITEMS">
 7         <id name="id" type="java.lang.Integer">
 8             <column name="ID" />
 9             <generator class="native" />
10         </id>
11         <property name="name" type="java.lang.String">
12             <column name="NAME" />
13         </property>
14         
15         <set name="categories" table="CATEGORIES_ITEMS" inverse="true">
16             <key>
17                 <column name="I_ID"></column>
18             </key>
19             <many-to-many class="Category" column="C_ID">
20             </many-to-many>
21         </set>
22         
23     </class>
24 </hibernate-mapping>

Item.hbm.xml

在Item与Category映射文件的配置中，两者应该交叉相同。如下：

 1 Category.hbm.xml
 2 <set name="items" table="CATEGORIES_ITEMS">
 3   <key>
 4     <column name="C_ID" />
 5   </key>
 6   <many-to-many class="Item" column="I_ID">
 7   </many-to-many>
 8 </set>
 9 
10 
11 Item.hbm.xml
12 <set name="categories" table="CATEGORIES_ITEMS" inverse="true">
13    <key>
14       <column name="I_ID"></column>
15    </key>
16    <many-to-many class="Category" column="C_ID">
17    </many-to-many>
18 </set>

（务必注意，双向多对多映射文件中，必须把其中一端的inverse设置为true，不让两端都维护关联关系，不然会造成主键冲突）

二、使用注意：

1.注意映射文件的配置。

（学习记录，错误不足之处，请您耐心指正^_^）