mybatis自增主键的问题

来源：互联网发布：erwin数据建模 pdf 编辑：程序博客网时间：2024/06/10 03:12

mybatis自增主键有个有意思的地方.在进行插入数据库操作时,新建一个不显式设定id的对象(对于int类型,此时id默认为0),然后执行save操作.该操作在将对象中属性存储在数据库表的同时,设定了该对象的id值,为mybatis自增的数值.而且,即使在新建对象的时候,显式设定了id的值,如new User(1,"tom"),在进行insert操作之后,该对象的id值也自动变为了mybatis自增的id值.这是mybatis内部的机制,不亲自试一下觉得这么轻易地就改变了对象的id值多多少少有些不可思议.

看代码:

1CREATE TABLE  user (

2  user_id int(10) unsigned NOT NULL auto_increment,

3  email_id varchar(45) NOT NULL,

4  password varchar(45) NOT NULL,

5  first_name varchar(45) NOT NULL,

6  last_name varchar(45) default NULL,

7  PRIMARY KEY  (user_id),

8  UNIQUE KEY Index_2_email_uniq (email_id)

9) ENGINE=InnoDB DEFAULT CHARSET=latin1;

01package com.sivalabs.mybatisdemo.domain;

02public class User

03{

04 private Integer userId;

05 private String emailId;

06 private String password;

07 private String firstName;

08 private String lastName;

09

10 @Override

11 public String toString() {

12  return 'User [userId=' + userId + ', emailId=' + emailId

13    + ', password=' + password + ', firstName=' + firstName

14    + ', lastName=' + lastName + ']';

15 }

16 //setters and getters

17}

01package com.sivalabs.mybatisdemo.mappers;

02

03import java.util.List;

04import com.sivalabs.mybatisdemo.domain.User;

05

06public interface UserMapper

07{

08

09 public void insertUser(User user);

10

11 public User getUserById(Integer userId);

12

13 public List<User> getAllUsers();

14

15 public void updateUser(User user);

16

17 public void deleteUser(Integer userId);

18

19}

30  <insert id='insertUser' parameterType='User' useGeneratedKeys='true' keyProperty='userId'>

31   INSERT INTO USER(email_id, password, first_name, last_name)

32    VALUES(#{emailId}, #{password}, #{firstName}, #{lastName})

33  </insert>

49    @Test

50    public void testInsertUser()

51    {

52     User user = new User();

53     user.setEmailId('test_email_'+System.currentTimeMillis()+'@gmail.com');

54     user.setPassword('secret');

55     user.setFirstName('TestFirstName');

56     user.setLastName('TestLastName');

57

58     userService.insertUser(user);

59  Assert.assertTrue(user.getUserId() != 0);

60  User createdUser = userService.getUserById(user.getUserId());

61  Assert.assertNotNull(createdUser);

62  Assert.assertEquals(user.getEmailId(), createdUser.getEmailId());

63  Assert.assertEquals(user.getPassword(), createdUser.getPassword());

64  Assert.assertEquals(user.getFirstName(), createdUser.getFirstName());

65  Assert.assertEquals(user.getLastName(), createdUser.getLastName());

66

67 }

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