MyBatis的Example类学习

原文链接：MyBatis的Example类详解

 

关于Example类的定义？

mybatis-generator会为每个字段产生Criterion，为底层的mapper.xml创建动态sql。如果表的字段比较多,产生的example类会十分庞大。理论上通过example类可以构造你想到的任何筛选条件。

在mybatis-generator中加以配置，配置数据表的生成操作就可以自动生成example了。这里对定义类型的不再过多解释，直接上干货。

 

 

 

1、查询：

  • selectByPrimaryKey
1 User user = UserMapper.selectByPrimaryKey("1001");
2 等同于：select * from user where id = "1001"

 

  • selectByExample (and条件)

 

1 Example example = new Example(User.class);
2 example.createCriteria().andEqualTo("id", "1001" )
3     .andEqualTo("userName", "小李");
4 User user = UserMapper.selectByExample(example);
5 
6 等同于：select * from user where id = "1001" and username = '小李'

 

  • selectByExample (or条件)

 

1 Example example = new Example(User.class);
2 example.or.andEqualTo("id", "1001" )
3 example.or.andEqualTo("userName", "小李");
4 User user = UserMapper.selectByExample(example);
5 
6 等同于：select * from user where id = "1001" or username = '小李'

 

  • selectByExample (and+or多条件查询)

 

1 Example example = new Example(User.class);
2         example.createCriteria().andEqualTo("id", "1" )
3                 .andEqualTo("userId", "1001");
4         example.and().orEqualTo("userName","小李")
5                 .orEqualTo("passWord","123");
6         List<User> user = UserMapper.selectByExample(example);
7 
8 等同于：
9 SELECT id,user_id,user_name,pass_word FROM user WHERE ( id = "1" and user_id = "1001" ) and ( user_name = "小李" or pass_word = "123" )

 

2、插入：

1 User user = new User();
2 user.setId("2");
3 user.setUserId("1002");
4 user.setUserName("小王");
5 user.setPassWord("666")
6 UserMapper.insert(user);
7 等同于：insert into user(id,user_id ,user_name,pass_word) values ('2','1002','小王','666');

 

3、更新：

  • updateByPrimaryKey
1 User user = new User();
2 user.setId("2");
3 user.setUserId("1002");
4 user.setUserName("小王");
5 user.setPassWord("666")
6 UserMapper.updateByPrimaryKey(user);
7 等同于：update user set user_id = "1002" user_name='小王', pass_word='666' where id='2'

 

  • updateByExampleSelective
 1 注意：updateByExample()更新所有的字段，包括字段为null的，建议使用 updateByExampleSelective()更新需要更新的字段
 2 
 3 Example example = new Example(User.class);
 4 example.createCriteria().andEqualTo("id","2");
 5 
 6 User user = new User();
 7 user.setUserName("小王");
 8 
 9 UserMapper.updateByExampleSelective(user,example);
10 
11 等同于：update user set user_name='小王' where id='2'

 

 

4、删除：

  •  deleteByPrimaryKey
1 UserMapper.deleteByPrimaryKey("1");  //相当于：delete from user where id="1"

 

  • deleteByExample
1 Example example = new Example(User.class);
2 example.createCriteria().andEqualTo("userId","1002");
3 UserMapper.deleteByExample(example);
4 等同于：delete from user where userId='1002'

 

5、查询数量：

1 Example example = new Example(User.class);
2 example.createCriteria().andEqualTo("id", "1001" )
3 
4 UserMapper.countByExample(example);
5 等同于：select count(*) from user where id='1001'

 

posted @ 2022-04-13 14:55  r1-12king  阅读(736)  评论(0)  编辑  收藏  举报