尝试hibernate annotations

最近开始尝试hibernate annotations，终于成功的将手上一个小应用转为annotations

1、spring orm support
与原来使用LocalSessionFactoryBean相比，变动不大（AnnotationSessionFactoryBean本来就是从LocalSessionFactoryBean类继承过来的嘛）

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 1    <bean
 2         id="sessionFactory"
 3         class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean"
 4         parent="AbstractSessionFactory">
 5         <property name="annotatedClasses">
 6             <list>
 7                 <value>xxx.xxx.xxx.domain.Accountvalue>
 8             list>
 9         property>
10     bean>
11     <bean
12         id="AbstractSessionFactory"
13         class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"
14         abstract="true">
15         <property
16             name="dataSource"
17             ref="DataSource" />
18         <property name="hibernateProperties">
19             <props>
20                 <prop key="hibernate.dialect">${hibernate.dialect}prop>
21                 <prop key="hibernate.show_sql">${hibernate.show_sql}prop>
22                 <prop key="hibernate.hbm2ddl.auto">${hibernate.hbm2ddl.auto}prop>
23                 <prop key="hibernate.cache.use_query_cache">${hibernate.cache.use_query_cache}prop>
24                 <prop key="hibernate.cache.provider_class">${hibernate.cache.provider_class}prop>
25             props>
26         property>
27         <property
28             name="lobHandler"
29             ref="DefaultLobHandler" />
30     bean>

2、id的配置
非常简单，在id的getter上面加个“@Id”就可以了。此时采用的id策略是javax.persistence.GenerationType.AUTO，也可以再加上“@GeneratedValue(generator =GenerationType.IDENTITY|GenerationType.SEQUENCE|GenerationType.TABLE)”换成其它策略。
我的应用采用的是hibernate的uuid策略，就不得不在这儿使用hibernate的扩展了

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->  @Id
  @Column(length = 32)
  @GeneratedValue(generator = "system-uuid")
  @GenericGenerator(name = "system-uuid", strategy = "uuid")

3、级联策略
在ejb3-persistence.jar中只定义了ALL、MERGE、PERSIST、REFRESH、REMOVE，比较恶心的就是，删除对象的时候，并不会级联删除关联对象，而是用update xx set parent_id=null where parent_id=?这类语句把关系干掉了事。不得已，在这儿用了hibernate的DELETE_ORPHAN。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->  @OneToMany(targetEntity = Attachment.class)
  @Cascade(value = {org.hibernate.annotations.CascadeType.DELETE_ORPHAN,
      org.hibernate.annotations.CascadeType.ALL})
  @JoinColumn(name = "info_id")

4、CACHE
ejb3-persistence.jar里面没有找到cache的配置，继续请出hibernate来干活

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;

@Entity
@Table(name = "T_INFO")
@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)

5、自定义字段类型
我的POJO中有一个private String content;的属性，按ejb3配成@Lob后，被处理成了text类型，text 64k的存储容量还是比较可怜了。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->  @Lob
  @Column(columnDefinition = "LongText")