四、ID生成策略 第一种：XML配置ID 通过为id元素增加generator子元素，该子元素拥有class属性。常用的class属性有: (1)increment:用于为long、short、或者int类型生成唯一标识。只有在没有其他进程往同一张表中插入数据的时候才能使用。在集群不要使用。（极
通过为
(1)increment:用于为long、short、或者int类型生成唯一标识。只有在没有其他进程往同一张表中插入数据的时候才能使用。在集群不要使用。（极少使用）
(2)native：让数据库自动选择identity，sequence，或者其他。
(3)uuid:128位的UUID算法，产生String类型ID
(4)identity：对于DB2、MySQL、SQL Server、Sybase和HypersonicSQL的内置标识字段提供支持。返回的标识符是long、short或者int类型。
sequence:在Oracel，PostgreSQL，SAP，DB，Mckio中使用序列（sequence），而在Interbase中使用生成器（generator），返回的标识符是long、short或者是int类型。
小实验1：
（1）创建Student.java
package com.zgy.hibernate.model; public class Student { private String id; private String name; private int age; private int score; public int getScore() { return score; } public void setScore(int score) { this.score = score; } public String getId() { return id; } public void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }
（2）在Student.hbm.xml中，为
（3）测试
package com.zgy.hibernate.model; import static org.junit.Assert.*; import java.util.Date; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.cfg.AnnotationConfiguration; import org.junit.AfterClass; import org.junit.BeforeClass; import org.junit.Test; public class HibernateIDTest { public static SessionFactory sf = null; @BeforeClass public static void beforeClass(){ sf = new AnnotationConfiguration().configure().buildSessionFactory(); } @Test public void testStudent() { Student s = new Student(); s.setName("张三"); s.setAge(20); s.setScore(90); Session session = sf.openSession(); session.beginTransaction(); session.save(s); session.getTransaction().commit(); session.close(); } @AfterClass public static void afterClass(){ sf.close(); } }
（4）验证
select * from student; +-----------------------------------------------+--------+------+------+ | id | name | age | score | +------------------------------------------------+------+-------+------+ | 4028dae54aa322d1014aa322d5a50000 | 张三 | 20 | 90 | +----------------------------------+------+-----+-------+------+------+ desc student;
数据插入成功，id类型为varchar(255)，主键
小实验2：
（1）修改Student.java。将id修改为int类型
package com.zgy.hibernate.model; public class Student { private int id; private String name; private int age; private int score; public int getScore() { return score; } public void setScore(int score) { this.score = score; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }
（2）在Student.hbm.xml中，为
（3）测试(删除student表)
（4）验证
select * from student; +----+------+-------+-------+ | id | name | age | score | +----+------+-------+-------+ | 1 | 张三 | 20 | 90 | +----+------+-----+--------+ desc student;
数据插入成功，id为int(11)类型，主键，Auto_increment
@GeneratedValue，默认的策略是auto,auto相当于XML中配置的native。
小实验1：
（1）编写Teacher.java。在getId()方法上添加@GeneratedValue
package com.zgy.hibernate.model; import java.util.Date; import javax.annotation.Generated; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.EnumType; import javax.persistence.Enumerated; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.Table; import javax.persistence.Temporal; import javax.persistence.TemporalType; import javax.persistence.Transient; @Entity @Table(name="_teacher") public class Teacher { private int id; private String name; private String title; private String address; private String wifeName; private Date birth; private ZhiCheng zhiCheng; @Id @GeneratedValue public int getId() { return id; } public void setId(int id) { this.id = id; } @Column(name="_name") public String getName() { return name; } public void setName(String name) { this.name = name; } public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public String getWifeName() { return wifeName; } public void setWifeName(String wifeName) { this.wifeName = wifeName; } @Temporal(TemporalType.DATE) public Date getBirth() { return birth; } public void setBirth(Date birth) { this.birth = birth; } @Enumerated(EnumType.STRING) public ZhiCheng getZhiCheng() { return zhiCheng; } public void setZhiCheng(ZhiCheng zhiCheng) { this.zhiCheng = zhiCheng; } }
（2）编写TeacherTesting.java，用于测试
package com.zgy.hibernate.model; import static org.junit.Assert.*; import java.util.Date; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.cfg.AnnotationConfiguration; import org.hibernate.cfg.Configuration; impo【本文来自鸿网互联 (http://www.68idc.cn)】rt org.junit.AfterClass; import org.junit.BeforeClass; import org.junit.Test; public class TeacherTesting { public static SessionFactory sf = null; @BeforeClass public static void beforeClass(){ sf = new AnnotationConfiguration().configure().buildSessionFactory(); } @Test public void test() { Teacher t = new Teacher(); t.setName("t1"); t.setTitle("高级"); t.setAddress("北京"); t.setBirth(new Date()); t.setZhiCheng(ZhiCheng.A); Session session = sf.openSession(); session.beginTransaction(); session.save(t); session.getTransaction().commit(); session.close(); } @AfterClass public static void afterClass(){ sf.close(); } }
（3）验证
select * from _teacher; desc _teacher;
数据插入成功，id为int(11)，主键，auto_increment
在使用Annotation的时候，除了使用auto策略，还可以使用increment,identity,sequence,table等等。
小实验2：
（1）修改Teacher.java.修改策略为identity
package com.zgy.hibernate.model; import java.util.Date; import javax.annotation.Generated; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.EnumType; import javax.persistence.Enumerated; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.Table; import javax.persistence.Temporal; import javax.persistence.TemporalType; import javax.persistence.Transient; @Entity @Table(name="_teacher") public class Teacher { private int id; private String name; private String title; private String address; private String wifeName; private Date birth; private ZhiCheng zhiCheng; @Id @GeneratedValue(strategy=GenerationType.IDENTITY) public int getId() { return id; } public void setId(int id) { this.id = id; } @Column(name="_name") public String getName() { return name; } public void setName(String name) { this.name = name; } public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public String getWifeName() { return wifeName; } public void setWifeName(String wifeName) { this.wifeName = wifeName; } @Temporal(TemporalType.DATE) public Date getBirth() { return birth; } public void setBirth(Date birth) { this.birth = birth; } @Enumerated(EnumType.STRING) public ZhiCheng getZhiCheng() { return zhiCheng; } public void setZhiCheng(ZhiCheng zhiCheng) { this.zhiCheng = zhiCheng; } }
（2）测试
（3）验证
select * from _teacher; desc _teacher;
使用table策略：
@javax.persistence.TableGenerator( name="Teacher_GEN", table="GENERATOR_TABLE", pkColumnName="pkkey", valueColumnName="pkvalue", pkColumnValue="Teacher", allocationSize=1 )
以上Annotation的意义：首先是定义了一个generator,该generator的名字叫做Teacher_GEN,生成一张表，表名为GENERATOR_TABLE，该表有两个字段，分别为pkColumnName和valueColumnName。这个表的第一条数据是：Teacher ， 1。其下一条数据的步长值，即Teacher表的下一条数据的值会是2
小实验3：
（1）修改Teacher.java类
package com.zgy.hibernate.model; import java.util.Date; import javax.annotation.Generated; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.EnumType; import javax.persistence.Enumerated; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.Table; import javax.persistence.Temporal; import javax.persistence.TemporalType; import javax.persistence.Transient; @Entity @javax.persistence.TableGenerator( name="Teacher_GEN", table="GENERATOR_TABLE", pkColumnName="pkkey", valueColumnName="pkvalue", pkColumnValue="Teacher", allocationSize=1 ) public class Teacher { private int id; private String name; private String title; private String address; private String wifeName; private Date birth; private ZhiCheng zhiCheng; @Id @GeneratedValue(strategy=GenerationType.TABLE,generator="Teacher_GEN") public int getId() { return id; } public void setId(int id) { this.id = id; } @Column(name="_name") public String getName() { return name; } public void setName(String name) { this.name = name; } public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public String getWifeName() { return wifeName; } public void setWifeName(String wifeName) { this.wifeName = wifeName; } @Temporal(TemporalType.DATE) public Date getBirth() { return birth; } public void setBirth(Date birth) { this.birth = birth; } @Enumerated(EnumType.STRING) public ZhiCheng getZhiCheng() { return zhiCheng; } public void setZhiCheng(ZhiCheng zhiCheng) { this.zhiCheng = zhiCheng; } }
（2）测试
（3）验证
查看hibernate执行过程中产生的sql语句
Hibernate: select pkvalue from GENERATOR_TABLE where pkkey = 'Teacher' for update
Hibernate: insert into GENERATOR_TABLE(pkkey, pkvalue) values('Teacher', ?)
Hibernate: update GENERATOR_TABLE set pkvalue = ? where pkvalue = ? and pkkey = 'Teacher'
Hibernate: select pkvalue from GENERATOR_TABLE where pkkey = 'Teacher' for update
Hibernate: update GENERATOR_TABLE set pkvalue = ? where pkvalue = ? and pkkey = 'Teacher'
Hibernate: insert into Teacher (address, birth, _name, title, wifeName, zhiCheng, id) values (?, ?, ?, ?, ?, ?, ?)
查看数据表
select * from generator_table; select * from teacher;
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