Hibernate多对多双向关联映射

                              Hibernate多对多双向关联映射

1、数据库结构

       category表：{ categoryId , categoryName }

       item表：{ itemId , itemName }

       category_item表：{ idCategory , idItem}

2、Category.hbm.xml

<hibernate-mapping>
    <class name="com.persistent.Category" table="category">
        <id name="id" column="categoryId" unsaved-value="null">
            <generator class="increment"></generator>
        </id>
        <property name="name" column="categoryName"></property>
        <set name="items" table="category_item" cascade="all" lazy="false">
            <key column="idCategory"></key>
            <many-to-many class="com.persistent.Item" column="idItem"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

3、Item.hbm.xml

<hibernate-mapping>
    <class name="com.persistent.Item" table="item">
        <id name="id" column="itemId" unsaved-value="null">
            <generator class="increment"></generator>
        </id>
        <property name="name" column="itemName"></property>
        <set name="categories" table="category_item" lazy="false" inverse="true">
            <key column="idItem"></key>
            <many-to-many class="com.persistent.Category" column="idCategory"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

4、Category.java和Item.java

public class Category ...{    
private Long id;
    private String name;
private Set items = new HashSet();
...
}

public class Item ...{
private Long id;
private String name;
private Set categories = new HashSet();
...
}
    

      映射文件中还可以不用set而用bag，只要把set出现的地方改成bag就行，这样相应的category.java和Item.java

文件当中就可以用List。