一、通用Mapper中的方法解析






















































方法 功能说明
int countByExample(UserExample example) thorws SQLException 按条件计数
int deleteByPrimaryKey(Integer id) thorws SQLException 按主键删除
int deleteByExample(UserExample example) thorws SQLException 按条件查询
String/Integer insert(User record) thorws SQLException 插入数据(返回值为ID)
User selectByPrimaryKey(Integer id) thorws SQLException 按主键查询
List selectByExample(UserExample example) thorws SQLException 按条件查询
List selectByExampleWithBLOGs(UserExample example) thorws SQLException 按条件查询(包括BLOB字段)。只有当数据表中的字段类型有为二进制的才会产生。
int updateByPrimaryKey(User record) thorws SQLException 按主键更新
int updateByPrimaryKeySelective(User record) thorws SQLException 按主键更新值不为null的字段
int updateByExample(User record, UserExample example) thorws SQLException 按条件更新
int updateByExampleSelective(User record, UserExample example) thorws SQLException 按条件更新值不为null的字段




### 二、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where后面的部分

java import tk.mybatis.mapper.entity.Example; Example example = new Example(JavaBean.class); Example.Criteria criteria = example.createCriteria();









































































方法 说明
example.setOrderByClause(“字段名 ASC”); 添加升序排列条件,DESC为降序
example.setDistinct(false) 去除重复,boolean型,true为选择不重复的记录。
criteria.andXxxIsNull 添加字段xxx为null的条件
criteria.andXxxIsNotNull 添加字段xxx不为null的条件
criteria.andXxxEqualTo(value) 添加xxx字段等于value条件
criteria.andXxxNotEqualTo(value) 添加xxx字段不等于value条件
criteria.andXxxGreaterThan(value) 添加xxx字段大于value条件
criteria.andXxxGreaterThanOrEqualTo(value) 添加xxx字段大于等于value条件
criteria.andXxxLessThan(value) 添加xxx字段小于value条件
criteria.andXxxLessThanOrEqualTo(value) 添加xxx字段小于等于value条件
criteria.andXxxIn(List<?>) 添加xxx字段值在List<?>条件
criteria.andXxxNotIn(List<?>) 添加xxx字段值不在List<?>条件
criteria.andXxxLike(“%”+value+”%”) 添加xxx字段值为value的模糊查询条件
criteria.andXxxNotLike(“%”+value+”%”) 添加xxx字段值不为value的模糊查询条件
criteria.andXxxBetween(value1,value2) 添加xxx字段值在value1和value2之间条件
criteria.andXxxNotBetween(value1,value2) 添加xxx字段值不在value1和value2之间条件

三、使用案例

1.查询

① selectByPrimaryKey() 按主键查询

//相当于:select * from user where id = 100;
User user = UserMapper.selectByPrimaryKey(100); 

② selectByExample() 和 selectByExampleWithBLOGs()

//相当于:select * from user where username = 'wyw' 
// and  username is null order by username asc,email desc
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("wyw");
criteria.andUsernameIsNull();
example.setOrderByClause("username asc,email desc");
List<?>list = XxxMapper.selectByExample(example);

2.插入数据

①insert()

//相当于:insert into user(ID,username,password,email) values 
//('dsfgsdfgdsfgds','jack','1234','hello@126.com');
User user = new User();
user.setId("dsfgsdfgdsfgds");
user.setUsername("jack");
user.setPassword("1234")
user.setEmail("hello@163.com");
XxxMapper.insert(user);

3.更新数据

①updateByPrimaryKey()

//相当于:update user set username='rose', password='5678', 
//email='hello@163.com' where id='a01'
User user =new User();
user.setId("a01");
user.setUsername("rose");
user.setPassword("5678");
user.setEmail("hello@163.com");
XxxMapper.updateByPrimaryKey(user);

②updateByPrimaryKeySelective()

//相当于:update user set password='7890' where id='a01'
User user = new User();
user.setId("a01");
user.setPassword("7890");
XxxMapper.updateByPrimaryKey(user);

③ updateByExample() 和 updateByExampleSelective()

//相当于:update user set password='6666' where username='jack'
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("jack");
User user = new User();
user.setPassword("6666");
XxxMapper.updateByPrimaryKeySelective(user,example);

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()

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

②deleteByExample()

//相当于:delete from user where username='jack'
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("jack");
XxxMapper.deleteByExample(example);

5.查询数据数量

①countByExample()

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

一个好奇的人