MyBatis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()

User user = XxxMapper.selectByPrimaryKey(100); //相当于select * from user where id = 100 1

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 1234567

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'); 1234567

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' 1234567

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' 12345

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' 1234567

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 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' 12345

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' 12345 <link href="https://csdnimg.cn/release/phoenix/mdeditor/markdown_views-778f64ae39.css" rel="stylesheet"> </div>