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一、mapper接口中的方法解析
mapper接口中的函數及方法

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
ListselectByExample(UserExample example) thorws SQLException?? ?按條件查詢
ListselectByExampleWithBLOGs(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用于添加條件，相當where后面的部分?
xxxExample example = new xxxExample();?
Criteria criteria = new 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字段等于value條件
criteria.andXxxNotEqualTo(value)?? ?添加xxx字段不等于value條件
criteria.andXxxGreaterThan(value)?? ?添加xxx字段大于value條件
criteria.andXxxGreaterThanOrEqualTo(value)?? ?添加xxx字段大于等于value條件
criteria.andXxxLessThan(value)?? ?添加xxx字段小于value條件
criteria.andXxxLessThanOrEqualTo(value)?? ?添加xxx字段小于等于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、應用舉例
1.查詢
① selectByPrimaryKey()

User user = XxxMapper.selectByPrimaryKey(100); //相當于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);
//相當于：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("wyw@163.com");
XxxMapper.insert(user);
//相當于：insert into user(ID,username,password,email) values ('dsfgsdfgdsfgds','admin','admin','wyw@126.com');

3.更新數據
①updateByPrimaryKey()

User user =new User();
user.setId("dsfgsdfgdsfgds");
user.setUsername("wyw");
user.setPassword("wyw");
user.setEmail("wyw@163.com");
XxxMapper.updateByPrimaryKey(user);
//相當于：update user set username='wyw', password='wyw', email='wyw@163.com' where id='dsfgsdfgdsfgds'

②updateByPrimaryKeySelective()

User user = new User();
user.setId("dsfgsdfgdsfgds");
user.setPassword("wyw");
XxxMapper.updateByPrimaryKey(user);
//相當于：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);
//相當于：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); ?//相當于：delete from user where id=1

②deleteByExample()

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

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轉自：https://blog.csdn.net/biandous/article/details/65630783?
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