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;
    }
    
}

Item.class

package com.zit.hibernate.n2n.both;

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

public class Item {
    
    private Integer id;
    private String name;
    
    private Set<Category> categories = new HashSet<>();

    
    public Set<Category> getCategories() {
        return categories;
    }
    public void setCategories(Set<Category> categories) {
        this.categories = categories;
    }
    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;
    }
    
}

{映射文件↓}

Category.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2015-12-25 13:55:35 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping package="com.zit.hibernate.n2n.both">
    <class name="Category" table="CATEGORIES">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" />
        </property>
        <set name="items" table="CATEGORIES_ITEMS">
            <key>
                <column name="C_ID" />
            </key>
            <many-to-many class="Item" column="I_ID">
            </many-to-many>
        </set>
    </class>
</hibernate-mapping>

Item.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2015-12-25 13:55:35 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping package="com.zit.hibernate.n2n.both">
    <class name="Item" table="ITEMS">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" />
        </property>
        
        <set name="categories" table="CATEGORIES_ITEMS" inverse="true">
            <key>
                <column name="I_ID"></column>
            </key>
            <many-to-many class="Category" column="C_ID">
            </many-to-many>
        </set>
        
    </class>
</hibernate-mapping>

在Item与Category映射文件的配置中，两者应该交叉相同。如下：

Category.hbm.xml
<set name="items" table="CATEGORIES_ITEMS">
  <key>
    <column name="C_ID" />
  </key>
  <many-to-many class="Item" column="I_ID">
  </many-to-many>
 8 </set>


Item.hbm.xml
<set name="categories" table="CATEGORIES_ITEMS" inverse="true">
   <key>
      <column name="I_ID"></column>
   </key>
   <many-to-many class="Category" column="C_ID">
   </many-to-many>
</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^_^）