Hibernate中ID生成策略 -电脑资料

电脑资料时间：2019-01-01 我要投稿

【meiwen.anslib.com - 电脑资料】

四、ID生成策略

第一种：XML配置ID

通过为元素增加子元素，该子元素拥有class属性，

Hibernate中ID生成策略

。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，为配置其generator的class为uuid

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

（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，为配置其generator的class为native

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

（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

第二种：Annotation配置ID

@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;

import 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，

电脑资料

《Hibernate中ID生成策略》(http://meiwen.anslib.com)。

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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