容器Map, List, Set, Bag都不仅可以映射值(String, Integer,FLoat, Double ...)类型, 还可以映射实体(我们自定义的pojo,有实体标记ID)类型.

映射值类型

考虑前面的Product对象,假如每个Product都配有几个图片(这通常是必需的)，新建一个表images (product_id, image_name, image_file) , product_id是外键， 和product的id关联。不打算给images表加入主键约束。如果按照one-to-many作一个对多映射,一个Product有多个image,这样做也可以,但是这样做的话需要做更多的工作: 要创建一个pojo Image, 然后要做映射文件,然后还要在Product的映射文件Product.hbm.xml中加入一对多映射.更简单的做法是:给Product加上一个属性images.是一个Map, key对应着image_name, value对应着image_file. 在Product的映射文件中只需要对这个map作一个映射:
public class Product { private int id; private String name; private float price; private Set orders; //映射map private Map images; // getters and setters ignored }

在Product.hbm.xml中队images作映射.

<hibernate-mapping> <class name="model.Product" table="pp" schema="etl" catalog="gssg_crms"> <id name="id" column="id"> <generator class="native" /> </id> <property name="name" type="java.lang.String"> <column name="name" length="50" not-null="true" /> </property> <property name="price" type="java.lang.Float"> <column name="price" precision="2" scale="0"/> </property> <!-- 多对多的映射中， 中间表table是必须指定的 --> <set name="orders" table="etl.order_line" cascade="save-update" fetch="join" lazy="false"> <key column="product_id" /> <many-to-many class="model.Order" column="order_id" /> </set> <map name="images" table="etl.images" cascade="all"> <key column="product_id" /> <index column="image_name" type="java.lang.String" /> <element column="image_file" type="java.lang.String" /> </map> </class> </hibernate-mapping> <!-- create table images( product_id int, image_name varchar(20) not null, image_file varchar(50) not null ) create table product( id int primary key, name varchar(50) not null, price float ) create table etl.order_line( order_id int, product_id int ) alter table images add constraint fk_image_product_id foreign key (product_id) references product(id) alter table order_line add constraint fk_orderline_order_id foreign key (order_id) references order(id) alter table order_line add constraint fk_orderline_product_id foreign key (product_id) references product(id) -->

写ProductDao,进行测试:
ProductDao: public interface ProductDao { public List list(); public Product getById(int id); public void delete(Product p); public void save(Product p); }

ProductHibernateDao: (带test case)
package dao.hibernate; import java.util.*; import java.util.Map.Entry; import org.hibernate.Transaction; import dao.ProductDao; import model.*; public class ProductHibernateDao extends BaseHibernateDao implements ProductDao { public List list() { return getSession().createQuery("from Product").list(); } public Product getById(int id) { return (Product) getSession().get(Product.class, id); } public void delete(Product p) { Transaction tx = getSession().beginTransaction(); getSession().delete(p); tx.commit(); } public void save(Product p) { Transaction tx = getSession().beginTransaction(); getSession().saveOrUpdate(p); tx.commit(); } //测试用例 public static void main(String[] args) { ProductDao dao = new ProductHibernateDao(); //测试查询 List<Product> list = dao.list(); System.out.println(list.size()); for(Product p1 : list){ System.out.println(p1); Iterator imgItr = p1.getImages().entrySet().iterator(); while(imgItr.hasNext()){ Entry e = (Entry)imgItr.next(); System.out.println(e.getKey() + " ### " + e.getValue()); } } //测试添加 Product p = dao.getById(7); Map map = new HashMap(); map.put("tea1", "tea1.jpg"); map.put("tea2", "tea2.jpg"); map.put("tea3", "tea3.jpg"); map.put("tea4", "tea4.jpg"); p.setImages(map); dao.save(p); //测试删除 Product p2 = dao.getById(4); p2.setImages(null); dao.save(p2); } }   

映射实体类型

上面采用值类型映射,是因为需要映射的字段就2个, 但是如果多于2个的话就不得不在Map里面放实体.为了放实体, 就需要有pojo Image, 它必须有id, 还要有映射文件.为了不更改表结构, 我们新建一个用来映射Image的表images1.

package model; public class Image { private int id; private String imageName; private String imageFile; public String toString(){ return "/nid: " + id + "/nimageName: " + imageName + "/nimageFile: " + imageFile; } //getters and setters ignored }

Image.hbm.xml

 <hibernate-mapping package="model"> <class name="Image" table="images1" schema="etl" catalog="gssg_crms"> <id name="id" column="id"> <generator class="native" /> </id> <property name="imageName" column="image_name" length="20" /> <property name="imageFile" column="image_File" length="50" /> </class> </hibernate-mapping> <!-- create table images1( id int primary key identity(1,1), product_id int, image_name varchar(20) not null, image_file varchar(50) not null ) alter table images1 add constraint fk_images1_product_id foreign key (product_id) references product(id) insert into images1(product_id, image_name, image_file) values(5, 'prod32', 'prod32.jpg') -->

修改一下Product.hbm.xml:

<hibernate-mapping> <class name="model.Product" table="pp" schema="etl" catalog="gssg_crms"> <id name="id" column="id"> <generator class="native" /> </id> <property name="name" type="java.lang.String"> <column name="name" length="50" not-null="true" /> </property> <property name="price" type="java.lang.Float"> <column name="price" precision="2" scale="0"/> </property> <set name="orders" table="etl.order_line" cascade="save-update" fetch="join" lazy="false"> <key column="product_id" /> <many-to-many class="model.Order" column="order_id" /> </set> <!--map中映射实体--> <map name="images" cascade="all"> <key column="product_id" /> <index column="image_name" type="java.lang.String" /> <one-to-many class="model.Image" /> </map> </class> </hibernate-mapping>

修改ProductHibernateDao的测试用例:

public static void main(String[] args) { ProductDao dao = new ProductHibernateDao(); List<Product> list = dao.list(); System.out.println(list.size()); for(Product p1 : list){ System.out.println(p1); Map<String, Image> map = p1.getImages(); Iterator itr = map.entrySet().iterator(); if(map!=null&&map.size()!=0){ System.out.println("############### images for this product ###############"); } while(itr.hasNext()){ Entry e = (Entry) itr.next(); System.out.println(e.getValue()); } }