一、通用Mapper中的方法解析

二、Example例項解析

mybatis的逆向工程中會生成例項及例項對應的example，example用於新增條件，相當where後面的部分

import tk.mybatis.mapper.entity.Example;

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

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.插入資料

①insert()

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

3.更新資料

①updateByPrimaryKey()

//相當於：update user set username='rose', password='5678', 
//email='[email protected]' where id='a01'
User user =new User();
user.setId("a01");
user.setUsername("rose");
user.setPassword("5678");
user.setEmail("[email protected]");
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()更新所有的欄位，包括欄位為null的也更新
建議使用 updateByExampleSelective()更新想更新的欄位

4.刪除資料

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.查詢資料數量

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);