hibernate学习(1) 事例

hibernate学习(一) 事例
1.maven 管理依赖 ??
mvn exec:java -Dexec.main-Dexec.args="store" //运行

2.javaBean
a)get,set 重构时的健壮性
b)private hibernate可直接访问
c)建表使用标识符 id ,set方法private,让hibernate分配标识符值
d)要无参数构造器(hibernate生成对象)
e)使用运行时代理,构造器修饰符>=package(没有字节码指令时,从持久化类获取数据更有效)
f)bidirectional safety method
public void addToEvent(Event event) {
this.getEvents().add(event);
//event.getParticipants().add(this);
}

3.映射文件(知道怎么加载(load),存储(store)持久化类
a)hibernate不从web加载,先在classpath查找(hibernate.jar)
b)映射文件的属性才被持久化
c)hibernate映射类型(java类型->数据库类型)有自动检测的功能
d)反射会占用资源,时间
e)连接池(内置(功能少),c3p0,proxool)
f)hbm2ddl create 创建表 (ant的schemaExport可把数据库schema重定向到文件)
g)session-factory 到一个数据库的全局factory
h)hibernate可自动detect 数据库方言
i)自动上下文
<property name="current_session_context_class">
thread
</property>
j)id native (oracle HIBERNATE_SEQUENCE 序列取值)

4.启动和辅助类
a)sessionFactory创建session(代表一个线程操作), factory线程安全,全局变量,只能实例化一次
private static final SessionFactory sessionFactory;

static {//静态块,类加载创建一次
try {
sessionFactory = new Configuration().configure().buildSessionFactory();
} catch (Throwable ex) {
System.err.println("Initial SessionFactory creation failed." + ex);
throw new ExceptionInInitializerError(ex);
}
}

public static SessionFactory getSessionFactory() {//获得唯一sessionFactory
return sessionFactory;
}
/////////////////////3.5方式-使用初始化private方法(类加载被jvm执行一次)
private static final SessionFactory sessionFactory = buildSessionFactory();

private static SessionFactory buildSessionFactory() {
try {
return new Configuration().configure().buildSessionFactory();
}
catch (Throwable ex) {
System.err.println("Initial SessionFactory creation failed." + ex);
throw new ExceptionInInitializerError(ex);
}
}

public static SessionFactory getSessionFactory() {
return sessionFactory;
}

b)在配置文件中给SessionFactory名称,hibernate创建后会给它绑定到jndi
(可用jmx容器实例化hibernateService,绑定到jndi)
c)getCurrentSession 第一次调用开始,绑定到线程,事务结束,会话与线程剥离,关闭session

5.关联
a)many2many
<set name="events" table="PERSON_EVENT" inverse="true">
<key column="PERSON_ID"/>
<many-to-many column="EVENT_ID" table="PERSON_EMAIL_ADDR">
<key column="PERSON_ID"/>
<element type="string" column="EMAIL_ADDR"/> 
</set>

c)关联方向(directionality),集合(collection),阶数(multiplicity)

d)many2many inverse="true" 可任意
many2one many一端 inverse="true" 忽略这一端关联,把这看成另一端的镜像

6.public package protected private

7.http get请求

8.session.save(e); 后获得主键
a)session.createQuery("from Event").list(); //返回全部
b) aPerson.getEmailAddresses().add(emailAddress);//直接用get方法赋值(HashSet())

9.hql
// If we want to handle it bidirectional and detached, we also need to load this
// collection with an eager outer-join fetch, this time with Criteria and not HQL:
Event anEvent = (Event) session
.createCriteria(Event.class).setFetchMode("participants", FetchMode.JOIN)
.add( Expression.eq("id", (long)1) )
.uniqueResult(); // Eager fetch the colleciton so we can use it detached
=======================================
Person aPerson = (Person) session
.createQuery("select p from Person p left join fetch p.events where p.id = :pid")
.setParameter("pid", (long)30)
.uniqueResult(); // Eager fetch the collection so we can use it detached

10.每个请求为一个session session-per-request getCurrentSession()自动绑定当前线程

11.auto-commit 自动提交

hibernate学习(1) 事例

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