MyBatis逆向工程中的Mapper接口以及Example的实例函数及详解

一、mapper接口中的方法解析

mapper接口中的函数及方法

方法功能说明
int countByExample(UserExample example) thorws SQLException按条件计数
int deleteByPrimaryKey(Integer id) thorws SQLException按主键删除
int deleteByExample(UserExample example) thorws SQLException按条件查询
String/Integer insert(User record) thorws SQLException插入数据(返回值为ID)
User selectByPrimaryKey(Integer id) thorws SQLException按主键查询
ListselectByExample(UserExample example) thorws SQLException按条件查询
ListselectByExampleWithBLOGs(UserExample example) thorws SQLException按条件查询(包括BLOB字段)。只有当数据表中的字段类型有为二进制的才会产生。
int updateByPrimaryKey(User record) thorws SQLException按主键更新
int updateByPrimaryKeySelective(User record) thorws SQLException按主键更新值不为null的字段
int updateByExample(User record, UserExample example) thorws SQLException按条件更新
int updateByExampleSelective(User record, UserExample example) thorws SQLException按条件更新值不为null的字段

二、example实例解析

mybatis的逆向工程中会生成实例及实例对应的example,example用于添加条件,相当where后面的部分
xxxExample example = new xxxExample();
Criteria criteria = new Example().createCriteria();

方法说明
example.setOrderByClause(“字段名 ASC”);添加升序排列条件,DESC为降序
example.setDistinct(false)去除重复,boolean型,true为选择不重复的记录。
criteria.andXxxIsNull添加字段xxx为null的条件
criteria.andXxxIsNotNull添加字段xxx不为null的条件
criteria.andXxxEqualTo(value)添加xxx字段等于value条件
criteria.andXxxNotEqualTo(value)添加xxx字段不等于value条件
criteria.andXxxGreaterThan(value)添加xxx字段大于value条件
criteria.andXxxGreaterThanOrEqualTo(value)添加xxx字段大于等于value条件
criteria.andXxxLessThan(value)添加xxx字段小于value条件
criteria.andXxxLessThanOrEqualTo(value)添加xxx字段小于等于value条件
criteria.andXxxIn(List<?>)添加xxx字段值在List<?>条件
criteria.andXxxNotIn(List<?>)添加xxx字段值不在List<?>条件
criteria.andXxxLike(“%”+value+”%”)添加xxx字段值为value的模糊查询条件
criteria.andXxxNotLike(“%”+value+”%”)添加xxx字段值不为value的模糊查询条件
criteria.andXxxBetween(value1,value2)添加xxx字段值在value1和value2之间条件
criteria.andXxxNotBetween(value1,value2)添加xxx字段值不在value1和value2之间条件

三、应用举例

1.查询

① selectByPrimaryKey()

<code class="hljs sql has-numbering"> 1 User user = XxxMapper.selectByPrimaryKey(100); //相当于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);
 //相当于:select * from user where username = 'wyw' and  username is null order by username asc,email desc
<code class="hljs vhdl has-numbering">&nbsp;

注:在iBator逆向工程生成的文件XxxExample.java中包含一个static的内部类Criteria,Criteria中的方法是定义SQL 语句where后的查询条件。

2.插入数据

①insert()

 User user = new User();
 user.setId("dsfgsdfgdsfgds");
 user.setUsername("admin");
 user.setPassword("admin")
 user.setEmail("wyw@163.com");
 XxxMapper.insert(user);
 //相当于:insert into user(ID,username,password,email) values ('dsfgsdfgdsfgds','admin','admin','wyw@126.com');

3.更新数据

①updateByPrimaryKey()

 User user =new User();
 user.setId("dsfgsdfgdsfgds");
 user.setUsername("wyw");
 user.setPassword("wyw");
 user.setEmail("wyw@163.com");
 XxxMapper.updateByPrimaryKey(user);
 //相当于: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);
 //相当于: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);
 //相当于:update user set password='wyw' where username='admin'

updateByExample()更新所有的字段,包括字段为null的也更新,建议使用 updateByExampleSelective()更新想更新的字段

4.删除数据

①deleteByPrimaryKey()

 XxxMapper.deleteByPrimaryKey(1); //相当于:delete from user where id=1 

②deleteByExample()

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

5.查询数据数量

①countByExample()

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