一、mapper介面中的方法解析

mapper介面中的函式及方法

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 
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

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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

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注：在iBator逆向工程生成的檔案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後的查詢條件。

2.插入資料

①insert()

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

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3.更新資料

①updateByPrimaryKey()

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

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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'

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

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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()

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

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5.查詢資料數量

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'