Hibernate学习笔记（二）【标识符及基本级联配置】
标识符
increment 用于代理主键.由Hibernate自增方式生成标识符,每次增量为1 identity 同上。由底层数据库生成标识符.前提是要数据库支持自增 sequence 同上。由底层数据库生成标识符.前提是要数据库支持序列 hilo 同上。由Hibernate根据high/low算法生成标识符 native 同上。根据数据库的支持，选择identity,sequence或hilo uuid.hex 同上。由Hibernate采用UUID算法生成字符串形式的标识符 assigned 用于自然主键。由Java代码通过setId()生成标识符。
数据库可使用的标识符
几种常用数据库可以使用的标识符生成器: 1. MySQL:identity,increment,hilo,native 2. MS SQL Server:identity,increment,hilo,native 3. Oracle:sequence,seqhilo,hilo,increment,native 4. 跨平台：native
IdentityTester.hbm.xml
<hibernate-mapping>
<class name="mypack.IdentityTester" table="IDENTITY_TESTER">
<id name="id" type="long" column="ID">
<generator class="identity"/>
</id>
<property name="name" type="string" column="NAME"/>
</class>
</hibernate-mapping>
IncrementTester.hbm.xml
<hibernate-mapping>
<class name="mypack.IncrementTester" table="INCREMENT_TESTER">
<id name="id" type="long" column="ID">
<meta attribute="scope-set">private</meta>
<generator class="increment"/>
</id>
<property name="name" type="string" column="NAME"/>
</class>
</hibernate-mapping>
NativeTester.hbm.xml
<hibernate-mapping>
<class name="mypack.NativeTester" table="NATIVE_TESTER">
<id name="id" type="long" column="ID">
<generator class="native"/>
</id>
<property name="name" type="string" column="NAME"/>
</class>
</hibernate-mapping>
HiloTester.hbm.xml 【101 201 301】
<hibernate-mapping>
<class name="mypack.HiloTester" table="HILO_TESTER">
<id name="id" type="long" column="ID">
<generator class="hilo">
<param name="table">hi_value</param>
<param name="column">next_value</param>
<param name="max_lo">100</param>
</generator>
</id>
<property name="name" type="string" column="NAME" />
</class>
</hibernate-mapping>
Squence.hbm.xml
<generator class="sequence”>
<param name="squence”>test_id_seq</param>
</generator>
基础级联 Monkey属于Team
Team.hbm.xml 【inverse="true" cascade="all-delete-orphan"】
<hibernate-mapping>
<class name="mypack.Team" table="TEAMS">
<id name="id" type="long" column="ID">
<generator class="increment"/>
</id>
<property name="name" type="string" column="NAME"/>
<set name="monkeys"
cascade="all-delete-orphan"
inverse="true">
<key column="TEAM_ID"/>
<one-to-many class="mypack.Monkey"/>
</set>
</class>
</hibernate-mapping>
Monkey.hbm.xml 【none delete all delete-orphan all-delete-orphan】
<hibernate-mapping>
<class name="mypack.Monkey" table="MONKEYS">
<id name="id" type="long" column="ID">
<generator class="increment"/>
</id>
<property name="name" type="string" column="NAME"/>
<!--mapping with cascade -->
<many-to-one
name="team"
column="TEAM_ID"
class="mypack.Team"
cascade="save-update" <!— none delete all delete-orphan all-delete-orphan -->
lazy="false" <!-- proxy -->
/>
</class>
</hibernate-mapping>
操作Service类代码片段
tx = session.beginTransaction();
Team team = new Team("BULL", new HashSet<Monkey>());
Monkey monkey = new Monkey();
monkey.setName("Tom");
monkey.setTeam(team);
team.getMonkeys().add(monkey);
session.save(team);
tx.commit();
tx =session.beginTransaction();
Team team =(Team) session.load(Team.class, teamId);
Monkey monkey =(Monkey) team.getMonkeys().iterator().next();
// 解除team和Monkey的关联关系
team.getMonkeys().remove(monkey);
monkey.setTeam(null);
tx.commit();