Question

For simplicity, let’s assume we have a single feed for all users.

The feed is just a list of articles.
Each user is free to favorite a certain article or remove it from their personal view.

User deleting an article does not affect other users; each user has its own “view” of the feed.

Simple Approach

A naïve scheme I devised is below:

(Of course, in the real application there is more to user-article relationship than just hiding or starring.)

The Problem

It looks like the link table entry should be created lazily, after the first change of options. Otherwise, when a new user signs up, or a new article pops up, we’d have to create a lot of empty link records, and also handle concurrency.

This means selecting a list of articles for a certain user is a query that combines:

• selecting all articles for which ArticleUserLink does not exist;
• selecting all articles for which ArticleUserLink exists and has is_hidden = 0.

Is OR the answer here, or is there a more effective database design / query to solve the problem?

Answer 1

how about using an inner query?

SELECT * 
FROM Article a
WHERE NOT EXISTS(SELECT * FROM ArticleUserLink WHERE article_id = a.id AND (is_hidden IS NULL OR is_hidden != 0))