MyBatis-Plus 入门代码，一个强大的单表查询工具包

    //查询
    public void selectCount() {
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.eq("name", "lqf");

        Integer count = mapper.selectCount(queryWrapper);
        System.out.println(count);
    }
    //删除，建议用update做逻辑删除
     public void delete() {
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper
                .isNull("name")
                .ge("age", 12)
                .isNotNull("email");
        int delete = mapper.delete(queryWrapper);
        System.out.println("delete return count = " + delete);
    }

public void save() {

        //修改值
        User user = new User();
        user.setStatus(true);
        user.setName("zhangsan");

        //修改条件，条件失败就是insert
        UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
        userUpdateWrapper.eq("name", "lqf");

        int update = mapper.saveOrUpdate(user, userUpdateWrapper);

        System.out.println(update);
    }