Hibernate技术解说

来源：www.45fan.com 2016-09-03 16:41:29

Hibernate技术解说

1、撰写数据库的定义

hibernate需要底层数据库的支持。我们为了测试也要求先建立数据库的相关表格，然后插入一些常用的数据来测试。

数据库的定义如下：

drop table TOY;

drop table CHILD;

drop table employers;

drop table employment_periods;

drop table employees;

create table CHILD (

ID NUMBER not null primary key

);

create table TOY (

TOY_ID NUMBER not null primary key,

CHILD_ID NUMBER ,

POSN NUMBER default 0,

NAME varchar(20) default '',

constraint FK_CHILD foreign key (CHILD_ID) references CHILD (ID)

);

DROP SEQUENCE SEQ_TOY;

DROP SEQUENCE SEQ_CHILD;

CREATE SEQUENCE "SEQ_TOY" INCREMENT BY 1 START WITH 1 MAXVALUE 1.0E28 MINVALUE 1 NOCYCLE CACHE 20 NOORDER;

CREATE SEQUENCE "SEQ_CHILD" INCREMENT BY 1 START WITH 1 MAXVALUE 1.0E28 MINVALUE 1 NOCYCLE CACHE 20 NOORDER;

主要做了这些工作：申明主键，申明外键，创建主键对应的sequence，注意我们采用的是oracle数据库。

2、好了，我们可以写一个ant脚本来编译我们的程序了

主要的target如下:

定义环境变量：

</fileset>

</path>

编译：

</target>

3、好了，我们现在可以使用我们的hibernate了。

例如我们插入一个Child，写了一个函数如下：

public int insertChild(Child c) throws HibernateException {

Transaction tx = null;

Session s = null;

try{

s = HibernateSessionFactory.openSession();

tx = s.beginTransaction();

s.save(c);

tx.commit();

}catch(HibernateException he){

if ( tx!=null ){

tx.rollback();

}

throw he;

}finally{

s.close();

}

return c.getId();

}

关键部分用红色标出。实际上我们调用了session类的save方法，session类还有很多其他的方法可以调用，如下：update,load,delete等等。传入一个类的引用，便可以保存了。作用类似于insert into …，然后我们的测试代码如下：

//首先实例化三个Toy类

Toy t1 = new Toy();

t1.setName("wawa1");

Toy t2 = new Toy();

t2.setName("wawa2");

Toy t3 = new Toy();

t3.setName("wawa3");

Toy[] toys1 = new Toy[] {t1,t2};

Toy[] toys2 = new Toy[] {t1,t2,t3};

Toy[] toys3 = new Toy[] {t1,t2};

Child c = new Child();

c.setToys(toys1);

ed.insert(c);//插入含有两个toy的Child

c = (Child)ed.findById(c.getClass(),1);//从数据库中取得这个Child类

this.assertEquals(2,c.getToys().length);//应该是两个toy

c.setToys(toys2);//重新设置toys属性

ed.update(c);//更新到数据库中

使用单元测试结果如下：

compile:

[echo] compiling...

test:

[echo] run test...

[java] .15:13:21,818 INFO Environment:378 - Hibernate 2.0 beta 6

[java] 15:13:21,878 INFO Environment:412 - loaded properties from resource hibernate.properties: {hibernate.connection.driver_class=oracle.jdbc.driver.OracleDriver, hibernate.cglib.use_reflection_optimizer=true, hibernate.dialect=net.sf.hibernate.dialect.OracleDialect, hibernate.jdbc.use_streams_for_binary=true, hibernate.jdbc.batch_size=0, hibernate.query.substitutions=true 1, false 0, yes 'Y', no 'N', hibernate.query.imports=net.sf.hibernate.test, net.sf.hibernate.eg, hibernate.connection.username=zhaocw, hibernate.connection.url=jdbc:oracle:thin:@CCSERVER:1521:oracle8i, hibernate.show_sql=true, hibernate.connection.password=zhaocw, hibernate.statement_cache.size=25, hibernate.connection.pool_size=10}

[java] 15:13:21,898 INFO Environment:426 - using java.io streams to persist binary types

[java] 15:13:21,898 INFO Environment:427 - using CGLIB reflection optimizer

[java] 15:13:21,928 INFO Environment:437 - JVM proxy support: true

[java] 15:13:21,938 INFO Configuration:689 - Configuration resource: /hibernate.cfg.xml

[java] 15:13:22,929 INFO Configuration:270 - Mapping resource: hibernate/Child.hbm.xml

[java] 15:13:23,170 INFO Collection:174 - Mapping class: hibernate.Child -> CHILD

[java] 15:13:23,340 INFO Configuration:270 - Mapping resource: hibernate/Toy.hbm.xml

[java] 15:13:23,420 INFO Collection:174 - Mapping class: hibernate.Toy -> TOY

[java] 15:13:24,411 INFO Configuration:871 - Configured SessionFactory: null

[java] 15:13:24,411 INFO Collection:976 - Mapping collection: hibernate.Child.toys -> TOY

[java] 15:13:25,242 INFO SessionFactoryImpl:140 - building session factory

[java] 15:13:25,262 INFO Dialect:37 - Using dialect: net.sf.hibernate.dialect.OracleDialect

[java] 15:13:25,272 INFO DriverManagerConnectionProvider:41 - Hibernate connection pool size: 10

[java] 15:13:25,292 INFO DriverManagerConnectionProvider:70 - using driver: oracle.jdbc.driver.OracleDriver at URL: jdbc:oracle:thin:@CCSERVER:1521:oracle8i

[java] 15:13:25,292 INFO DriverManagerConnectionProvider:71 - connection properties: {user=zhaocw, password=zhaocw}

[java] 15:13:25,323 INFO PreparedStatementCache:60 - prepared statement cache size: 25

[java] 15:13:25,333 INFO SessionFactoryImpl:170 - Use outer join fetching: true

[java] 15:13:26,033 INFO SessionFactoryImpl:193 - Use scrollable result sets: true

[java] 15:13:26,033 INFO SessionFactoryImpl:202 - echoing all SQL to stdout

[java] 15:13:27,145 INFO SessionFactoryObjectFactory:82 - no JDNI name configured

[java] 15:13:27,145 INFO SessionFactoryImpl:287 - Query language substitutions: {no='N', true=1, yes='Y', false=0}

[java] Hibernate: select SEQ_CHILD.nextval from dual

[java] Hibernate: select SEQ_TOY.nextval from dual

[java] Hibernate: insert into CHILD (id) values (?)

[java] Hibernate: insert into TOY (name, TOY_ID) values (?, ?)

[java] Hibernate: update TOY set CHILD_ID=?, POSN=? where TOY_ID=?

[java] Hibernate: select child0_.id as id from CHILD child0_ where child0_.id=?

[java] Hibernate: select toy0_.TOY_ID as TOY_ID__, toy0_.POSN as POSN__, toy0_.TOY_ID as TOY_ID, toy0_.name as name from TOY toy0_ where toy0_.CHILD_ID=?

[java] Hibernate: select SEQ_TOY.nextval from dual

[java] Hibernate: insert into TOY (name, TOY_ID) values (?, ?)

[java] Hibernate: update TOY set name=? where TOY_ID=?

[java] Hibernate: update TOY set CHILD_ID=null, POSN=null where CHILD_ID=?

[java] Hibernate: update TOY set CHILD_ID=?, POSN=? where TOY_ID=?

[java] Hibernate: select child0_.id as id from CHILD child0_ where child0_.id=?

[java] Hibernate: select toy0_.TOY_ID as TOY_ID__, toy0_.POSN as POSN__, toy0_.TOY_ID as TOY_ID, toy0_.name as name from TOY toy0_ where toy0_.CHILD_ID=?

[java] Hibernate: delete from TOY where TOY_ID=?

[java] Hibernate: update TOY set name=? where TOY_ID=?

[java] Hibernate: update TOY set CHILD_ID=null, POSN=null where CHILD_ID=?

[java] Hibernate: update TOY set CHILD_ID=?, POSN=? where TOY_ID=?

[java] Time: 6.269

[java] OK (1 test)

可以看见实际上hibernate执行的sql语句，测试结果是成功的。

五、总结

实际上，Hibernate可以实现多层次继承的架构，经常用到的包括<many-to-one>,<one-to-many>,<one-to-one>,<subclass>,<joined-subclass>等等。还有组件功能<component>可以让某个属性类存储在父类中。总之，Hibernate功能十分强大，效率也非常搞。建议大家在使用的过程中不断的总结经验，最好能够分享自己的经验。

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Hibernate技术解说

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