Question

Few words about my idea

Working on some web based, education project. Creating question-answer system for this project. There is some logical difficulties that I can’t figure out:

There are teachers and students between users. Every student selects some course during signup.

I have 5 tables: users, courses, lessons, questions, answers.

There might be 2 types of questions:

1. User based. For ex, when teacher wants to send questions to specific users and vise-versa (users may post question to teachers too).

2. Course-lesson combination based. For ex, teacher wants to post questions to all course listeners based on lesson, they are currently in.

What I’ve done

I’ve created questions from-to (qft) table

CREATE TABLE `questions from-to` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `qid` int(11) unsigned NOT NULL,
  `from_uid` int(11) unsigned NOT NULL,
  `to_uid` int(11) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  KEY `qft.from_uid_users.id` (`from_uid`),
  KEY `qft.to_uid_users.id` (`to_uid`),
  KEY `qft.qid_qe.id` (`qid`),
  CONSTRAINT `qft.from_uid_users.id` FOREIGN KEY (`from_uid`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `qft.qid_qe.id` FOREIGN KEY (`qid`) REFERENCES `questions_and_exercises` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `qft.to_uid_users.id` FOREIGN KEY (`to_uid`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8

Which looks like that

• qid – is question id, connects this table with questions, based
  on id
• from_uid – from user id (question sender id), connects this table with users, based
  on id
• to_uid – to user id (question receiver id), connects this table with users, based
  on id

So I tried to create some universal solution for both:

• students and teacher so they can post questions to each others. ok

• teacher can post to some users specific questions. ok

BUT there is a problem

The problem is

What if, teacher wants to post question for all course listeners? I already have user-course relationship table, but, currently I need to add one-by-one user id’s into questions from-to table so they can receive questions. I have no idea, how can I design this table for both situations: for "mass questioning" based on course-lesson combination and for "user-user" type question posting (teacher sends questions to specific students and vise-versa)

Any suggestions?

Answer 1

One possibility would be to have a special code in to_uid that your application knows to interpret as “show to all users.” When it encounters a to_uid of -1 (or whatever you chose) then it does a select for all students listening to that course, and displays the question just as if their IDs had all been separately listed in to_uid. Depending on how your application is organized, you should only have to implement this special check in a small number of places.