Hibernate之第4解之-hibernate_集合映射

hibernate的集合映射demo：

前提介紹：

      書籍Book【id,name,authors】，authors可能有N個，所以這裡用set表示；

      實體類一個Book；表呢有兩個：tbook、tauthors；

1：model：

package model;import java.util.Set;public class Book {private int id;private String name;private Set<String> authors;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Set<String> getAuthors() {return authors;}public void setAuthors(Set<String> authors) {this.authors = authors;}}

 2：Book的對應檔：hbm.xml

<class name="Book" table="TBook" lazy="false">        <id name="id">            <generator class="native"/>        </id>        <property name="name" column="bookName"/>        <set name="authors" table="TAuthors">        <key column="id" />        <element column="authorName" type="string" not-null="true" length="30"/>        </set>    </class>

     這裡有兩個地方需要稍微注意：

    *寫明not-null="true"產生tauthors表時才會自動為你產生主鍵【id，authorName】，否則表沒有主鍵；

    *指定length="30"如果不指定，會有以下ERROR，主鍵產生失敗；所以要指定小些；

 not-null="true" length="30"

1218 [main] ERROR org.hibernate.tool.hbm2ddl.SchemaUpdate - Unsuccessful: create table TAuthors (id integer not null, topicName varchar(255) not null, primary key (id, topicName))1218 [main] ERROR org.hibernate.tool.hbm2ddl.SchemaUpdate - Specified key was too long; max key length is 767 bytes

 3.DAO：

/** add */public void addPerson(Book p){Session session=null;Transaction tran=null;try {session=HibernateUtil.getSession();tran=session.beginTransaction();session.save(p);tran.commit();} catch (HibernateException e) {tran.rollback();e.printStackTrace();}finally{if(session!=null && session.isOpen()){session.close();}}}

 4：service：

        BookDao dao=new BookDao();/** add */public void add(Book p){dao.addPerson(p);}

 5：JUnit 測試：

@Test public void testAdd() {Book p=new Book();p.setName("《Java核心技術》");Set<String> authors=new HashSet<String>();authors.add("Cay S.Horstmann");authors.add("Gary Cornell");p.setAuthors(authors);manager.add(p);}

 6：最終資料庫結果：

mysql> select * from tbook;+----+------------------+| id | bookName         |+----+------------------+|  1 | 《Java核心技術》 |+----+------------------+1 row in setmysql> select * from tauthors;+----+-----------------+| id | authorName      |+----+-----------------+|  1 | Cay S.Horstmann ||  1 | Gary Cornell    |+----+-----------------+2 rows in set

 表的ddl語句：

CREATE TABLE `tbook` (  `id` int(11) NOT NULL AUTO_INCREMENT,  `bookName` varchar(255) DEFAULT NULL,  PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8--------------------------------------------------------------------CREATE TABLE `tauthors` (  `id` int(11) NOT NULL,  `authorName` varchar(30) NOT NULL,  PRIMARY KEY (`id`,`authorName`),  KEY `FK529261547AAF8BC9` (`id`),  CONSTRAINT `FK529261547AAF8BC9` FOREIGN KEY (`id`) REFERENCES `tbook` (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8

 That's all;