mybatis-plus 条件构造器 Wrapper

官网：https://mp.baomidou.com/guide/wrapper.html

作用：用于写复杂的SQL

案例

一、排序

    @Test
    public void orderWrapper(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.orderByDesc("id");
        List<User> userList = userMapper.selectList(wrapper);
        for (User user : userList) {
            System.out.println(user);
        }
    }

二、模糊查询

    @Test
    public void likeWrapper(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper
//                like %a%
                .like("name","a");
//                .likeRight("email","@");
        User user = userMapper.selectOne(wrapper);
        System.out.println(user);
    }

三、子查询

    @Test
    public void sonWrapper(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.inSql("id", "select id from user where id < 6");
        List<User> userList = userMapper.selectList(wrapper);
        for (User user : userList) {
            System.out.println(user);
        }
    }

四、between and

    @Test
    public void betweenWrapper(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.between("age", "10", "23");
        List<User> userList = userMapper.selectList(wrapper);
        for (User user : userList) {
            System.out.println(user);
        }
    }

五、查询条件

与通过Map查询作用相似

    @Test
    public void searchWrapper(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.eq("name", "wt");
        Integer count = userMapper.selectCount(wrapper);
        System.out.println(count);
    }