Example.Criteria

1.example实例解析

mybatis的逆向工程中会生成实例及实例对应的example，example用于添加条件，相当于where后面的部分

criteria.andXxxEqualTo(value)             添加Xxx字段等于value的条件  

2.应用举例

1.查询

① selectByPrimaryKey()
User user = XxxMapper.selectByPrimaryKey(100); //相当于select * from user where id = 100
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② selectByExample() 和 selectByExampleWithBLOGs()
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();//Criteria是Example类的一个静态内部类，用来存储查询条件语句
criteria.andUsernameEqualTo("wyw");//添加Username字段等于wyw的条件  
criteria.andUsernameIsNull();
example.setOrderByClause("username asc,email desc");
List<?>list = XxxMapper.selectByExample(example);
//相当于：select * from user where username = ‘wyw‘ and  username is null order by username asc,email desc
注：在iBator逆向工程生成的文件XxxExample.java中包含一个static的内部类Criteria，Criteria中的方法是定义SQL 语句where后的查询条件。

2.插入数据

①insert()
User user = new User();
user.setId("dsfgsdfgdsfgds");
user.setUsername("admin");
user.setPassword("admin")
user.setEmail("wyw@163.com");
XxxMapper.insert(user);
//相当于：insert into user(ID,username,password,email) values (‘dsfgsdfgdsfgds‘,‘admin‘,‘admin‘,‘wyw@126.com‘);

3.更新数据

①updateByPrimaryKey()
User user =new User();
user.setId("dsfgsdfgdsfgds");
user.setUsername("wyw");
user.setPassword("wyw");
user.setEmail("wyw@163.com");
XxxMapper.updateByPrimaryKey(user);
//相当于：update user set username=‘wyw‘, password=‘wyw‘, email=‘wyw@163.com‘ where id=‘dsfgsdfgdsfgds‘
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②updateByPrimaryKeySelective()
User user = new User();
user.setId("dsfgsdfgdsfgds");
user.setPassword("wyw");
XxxMapper.updateByPrimaryKey(user);
//相当于：update user set password=‘wyw‘ where id=‘dsfgsdfgdsfgds‘
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③ updateByExample() 和 updateByExampleSelective()
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("admin");
User user = new User();
user.setPassword("wyw");
XxxMapper.updateByPrimaryKeySelective(user,example);
//相当于：update user set password=‘wyw‘ where username=‘admin‘
updateByExample()更新所有的字段，包括字段为null的也更新，建议使用 updateByExampleSelective()更新想更新的字段

4.删除数据

①deleteByPrimaryKey()
XxxMapper.deleteByPrimaryKey(1);  //相当于：delete from user where id=1
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②deleteByExample()
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("admin");
XxxMapper.deleteByExample(example);
//相当于：delete from user where username=‘admin‘

5.查询数据数量

①countByExample()
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("wyw");
int count = XxxMapper.countByExample(example);
//相当于：select count(*) from user where username=‘wyw‘

Example.Criteria