MybatisPlus使用Wrapper实现条件查询功能

//查询name不为空的用户，并且邮箱不为空的用户，年龄大于等于12
 @Test
 void selectBy01(){
 ​
     QueryWrapper<User> wrapper=new QueryWrapper<>();
     wrapper
             .isNotNull("name") //name不为空的用户
             .isNotNull("email") //邮箱不为空的用户
             .ge("age",12); //年龄大于等于12
 ​
     userMapper.selectList(wrapper).forEach(System.out::println);
 }

//查询name为 "Jone" 的用户
 @Test
 void selectBy02(){
 ​
     QueryWrapper<User> wrapper=new QueryWrapper<>();
     wrapper.eq("name","Jone"); //name为 "Jone" 的用户
 ​
     //查询一个数据，为多个用 selectList 或者 selectByMap
     User user = userMapper.selectOne(wrapper);
 ​
     System.out.println(user);
 }

//查询 10 到 20 岁的用户数
 @Test
 void selectBy03(){
     QueryWrapper<User> wrapper=new QueryWrapper<>();
     wrapper.between("age",10,20);
 ​
     Integer count = userMapper.selectCount(wrapper);
     //查询 10 到 20 岁的用户的结果数
 ​
     System.out.println(count);
 }

@Test
 void selectLike01(){
     QueryWrapper<User> wrapper=new QueryWrapper<>();
     wrapper
             .notLike("name","To") //名字不包含 To
             .like("name","o") //名字包含 o 的
             //左和右 左：%e   右：e%  两边：%e%
             //右查询
             .likeRight("email","test");
 ​
     List<Map<String, Object>> users = userMapper.selectMaps(wrapper);
     users.forEach(System.out::println);
 }

@Test
 void selectLike02(){
     QueryWrapper<User> wrapper=new QueryWrapper<>();
     wrapper
             //一个SQL语句写的子查询
             .inSql("id","select id from user where age<20");
 ​
     List<Object> users = userMapper.selectObjs(wrapper);
     users.forEach(System.out::println);
 }

@Test
 void selectLike03(){
     QueryWrapper<User> wrapper=new QueryWrapper<>();
     //降序排序
     wrapper.orderByDesc("id");
     //升序排序
     //wrapper.orderByAsc("id");
 ​
     List<User> users = userMapper.selectList(wrapper);
     users.forEach(System.out::println);
 }