MyBatis的Mapper接口以及Example的實例函數及詳解

一、mapper接口中的方法解析
mapper接口中的函數及方法

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
xxxExample example = new xxxExample();
Criteria criteria = new Example().createCriteria();

三、應用舉例

1.查詢

① selectByPrimaryKey()

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

② selectByExample() 和 selectByExampleWithBLOGs()

UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("wyw");
criteria.andUsernameIsNull();
example.setOrderByClause("username asc,email desc");
List<?>list = XxxMapper.selectByExample(example);
//相當於：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中包含一個static的內部類Criteria，Criteria中的方法是定義SQL 語句where后的查詢條件。

2.插入數據

①insert()

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

3.更新數據

①updateByPrimaryKey()

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

②updateByPrimaryKeySelective()

User user = new User();
user.setId("dsfgsdfgdsfgds");
user.setPassword("wyw");
XxxMapper.updateByPrimaryKey(user);
//相當於：update user set password='wyw' where id='dsfgsdfgdsfgds'

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);
//相當於：update user set password='wyw' where username='admin'

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()

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

②deleteByExample()

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

 

5.查詢數據數量

①countByExample()

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