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 = 10
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
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'
