Hibernate主键生成策略

1.increment

适用于代理主键。由hibernate自动以递增的方式生成表识符，每次增量为1。
     mysql
     Hibernate: select max(id) from users
     Hibernate: insert into hjd.users (name, pass, sex, id) values (?, ?, ?, ?)
   适用于所有的数据库。

2.identity

适用于代理主键。由底层数据库生成表识符。条件是数据库支持自动增长数据类型。
      Hibernate: insert into hjd.users (name, pass, sex) values (?, ?, ?)
      适用于mysql   DB2 SQLServer Sybase等

sequence   适用于代理主键。Hibernate根据底层数据库序列生成标识符。条件是数据库支持序列。
         DB2 Oracle 等

3.hilo

适用于代理主键。Hibernate根据hign/low算法生成标识符。Hibernate把特定表的字段作为“hign”值。默认情况下，采用hibernate_unique_key表的next_hi字段。

　　　　<generator class="hilo">
               <param name="table">hilo_ids</param>
               <param name="column">value</param>
               <param name="max_lo">100</param>
           </generator>

Hibernate: create table hilo_ids ( value integer )
Hibernate: insert into hilo_ids values ( 0 )
四月 24, 2015 2:37:56 下午 org.hibernate.tool.hbm2ddl.SchemaExport execute
INFO: HHH000230: Schema export complete
Hibernate: select value from hilo_ids for update
Hibernate: update hilo_ids set value = ? where value = ?
Hibernate: insert into hjd.users (name, pass, sex, id) values (?, ?, ?, ?)

4.native

适用于代理主键。根据底层数据库对自动生成表示符的能力来选择identity、sequence、hilo

5.uuid.hex

适用于代理主键。Hibernate采用128位的UUID算法来生成标识符。该算法能够在网络环境中生成唯一的字符串标识符，这种策略并不流行，因为字符串类型的主键比整数类型的主键占用更多的数据库空间。

6.assigned

适用于自然主键。由java程序负责生成标识符。不能把setID()方法声明为private的。尽量避免使用自然主键。

public class Dept implements Serializable{

   private static final long serialVersionUID = 1L;
   private String name;
   private Date cdate;
   public Dept() {
       super();
       // TODO Auto-generated constructor stub
   }
   public String getName() {
       return name;
   }
   public void setName(String name) {
       this.name = name;
   }
   public Date getCdate() {
       return cdate;
   }
   public void setCdate(Date cdate) {
       this.cdate = cdate;
   }
}
<class name="Dept" table="depts" catalog="hjd">
       
       <id name="name" column="name" type="string">
       <generator class="assigned"/>
       </id>
       
       <property name="cdate" column="cdate" type="date"/>
   </class>

7.复合主键：

第一种写法

public class Customer implements Serializable {

   private static final long serialVersionUID = 1L;
   private String firstName;
   private String lastName;
   private String sex;
   public Customer() {
       super();
       // TODO Auto-generated constructor stub
   }
   public String getFirstName() {
       return firstName;
   }
   public void setFirstName(String firstName) {
       this.firstName = firstName;
   }
   public String getLastName() {
       return lastName;
   }
   public void setLastName(String lastName) {
       this.lastName = lastName;
   }
   public String getSex() {
       return sex;
   }
   public void setSex(String sex) {
       this.sex = sex;
   }
}

<hibernate-mapping package="hiber01.domain">
   <class name="Customer" table="customers" catalog="hjd">
       <composite-id>
           <key-property name="firstName" length="50" type="string"/>
           <key-property name="lastName" length="50" type="string"/>
       </composite-id>
       <property name="sex" length="4"></property>
   </class>
</hibernate-mapping>

@Test
   public void save() {
       // 1.获取Configuration对象
       Configuration configuration = new Configuration().configure();
       // 2.获取SessionFactory对象
       SessionFactory sessionFactory = configuration.buildSessionFactory();
       // 3.获取session，打开事务
       Session session = sessionFactory.openSession();
       Transaction ts = session.beginTransaction();
       Customer customer=new Customer();
       customer.setFirstName("zz");
       customer.setLastName("sf");
       customer.setSex("女");

       try {
           session.save(customer);
       } catch (Exception e) {
           ts.rollback();
           e.printStackTrace();
       }
       ts.commit();
       session.close();
   }

第二种写法：

public class Customer implements Serializable {

   private static final long serialVersionUID = 1L;
   private CustomerId customerId;
   private String sex;
   public Customer() {
       super();
       // TODO Auto-generated constructor stub
   }
   public CustomerId getCustomerId() {
       return customerId;
   }
   public void setCustomerId(CustomerId customerId) {
       this.customerId = customerId;
   }
   public String getSex() {
       return sex;
   }
   public void setSex(String sex) {
       this.sex = sex;
   }
}

public class CustomerId implements Serializable{
   private static final long serialVersionUID = 1L;
   private String firstName;
   private String lastName;
   public CustomerId() {
       super();
       // TODO Auto-generated constructor stub
   }
   public String getFirstName() {
       return firstName;
   }
   public void setFirstName(String firstName) {
       this.firstName = firstName;
   }
   public String getLastName() {
       return lastName;
   }
   public void setLastName(String lastName) {
       this.lastName = lastName;
   }
}

注意：两个类都需要实现可序列化接口，否则会报错