MyBatis中通用Mapper接口以及Example的方法解析

一、通用Mapper中的方法解析

方法	功能說明
int countByExample(UserExample example) thorws SQLException	按條件計數
int deleteByPrimaryKey(Integer id) thorws SQLException	按主鍵刪除
int deleteByExample(UserExample example) thorws SQLException	按條件查詢
String/Integer insert(User record) thorws SQLException	插入數據（返回值為ID）
User selectByPrimaryKey(Integer id) thorws SQLException	按主鍵查詢
List selectByExample(UserExample example) thorws SQLException	按條件查詢
List selectByExampleWithBLOGs(UserExample example) thorws SQLException	按條件查詢（包括BLOB字段）。只有當數據表中的字段類型有為二進制的才會產生。
int updateByPrimaryKey(User record) thorws SQLException	按主鍵更新
int updateByPrimaryKeySelective(User record) thorws SQLException	按主鍵更新值不為null的字段
int updateByExample(User record, UserExample example) thorws SQLException	按條件更新
int updateByExampleSelective(User record, UserExample example) thorws SQLException	按條件更新值不為null的字段

二、Example實例解析

mybatis的逆向工程中會生成實例及實例對應的example，example用於添加條件，相當where后面的部分

import tk.mybatis.mapper.entity.Example;

Example example = new Example(JavaBean.class);
Example.Criteria criteria = example.createCriteria();

方法	說明
example.setOrderByClause(“字段名 ASC”);	添加升序排列條件，DESC為降序
example.setDistinct(false)	去除重復，boolean型，true為選擇不重復的記錄。
criteria.andXxxIsNull	添加字段xxx為null的條件
criteria.andXxxIsNotNull	添加字段xxx不為null的條件
criteria.andXxxEqualTo(value)	添加xxx字段等於value條件
criteria.andXxxNotEqualTo(value)	添加xxx字段不等於value條件
criteria.andXxxGreaterThan(value)	添加xxx字段大於value條件
criteria.andXxxGreaterThanOrEqualTo(value)	添加xxx字段大於等於value條件
criteria.andXxxLessThan(value)	添加xxx字段小於value條件
criteria.andXxxLessThanOrEqualTo(value)	添加xxx字段小於等於value條件
criteria.andXxxIn(List<？>)	添加xxx字段值在List<？>條件
criteria.andXxxNotIn(List<？>)	添加xxx字段值不在List<？>條件
criteria.andXxxLike(“%”+value+”%”)	添加xxx字段值為value的模糊查詢條件
criteria.andXxxNotLike(“%”+value+”%”)	添加xxx字段值不為value的模糊查詢條件
criteria.andXxxBetween(value1,value2)	添加xxx字段值在value1和value2之間條件
criteria.andXxxNotBetween(value1,value2)	添加xxx字段值不在value1和value2之間條件

三、使用案例

1.查詢

① selectByPrimaryKey() 按主鍵查詢

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

② selectByExample() 和 selectByExampleWithBLOGs()

//相當於：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.插入數據

①insert()

//相當於：insert into user(ID,username,password,email) values 
//('dsfgsdfgdsfgds','jack','1234','[e-mail]');
User user = new User();
user.setId("dsfgsdfgdsfgds");
user.setUsername("jack");
user.setPassword("1234")
user.setEmail("[e-mail]");
XxxMapper.insert(user);

3.更新數據

①updateByPrimaryKey()

//相當於：update user set username='rose', password='5678', 
//email='[e-mail]' where id='a01'
User user =new User();
user.setId("a01");
user.setUsername("rose");
user.setPassword("5678");
user.setEmail("[e-mail]");
XxxMapper.updateByPrimaryKey(user);

②updateByPrimaryKeySelective()

//相當於：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()

//相當於：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，包括字段為null的也更新
建議使用 updateByExampleSelective()更新想更新的字段

4.刪除數據

①deleteByPrimaryKey()

//相當於：delete from user where id=1
XxxMapper.deleteByPrimaryKey(1);  

②deleteByExample()

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

5.查詢數據數量

①countByExample()

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