SQL 数据库设计问题 android 房间数据库

Question

I'm building an app that fetches timeline posts (as in social media app) from server, save it to local room db and show them to UI via paging. My issue is, on what crteria, i should fetch posts from local db?

Approach i've tried:

1. Fetch posts based on post id (primary key) descending, but it fails in below case

Suppose User A has 2 posts. Later, user B create 2 posts (thus, having newer postId). Now, when user B follows User A, backend will return posts in this format: 2 post of user A + 2 posts of user B. but (saving and) fetching posts from local db based on postId descending would make post of user B to appear below post of user A in user A's timeline, which seems incorrect. Same could be thought for ascending order in reverse case.

2.Use a timestamp column in db corresponding to insertion time of post in db and fetch posts based on timestamp. But all post in batch insertion get same value, whether its Instant.now() or System.currentTimeMillis()

Answer 1

first option is correct, fetch posts based on post id (primary key) descending. I think your case is incorrect, see example: A posts 1, 2 B posts 3, 4 B follow's A so his timeline would fetch from local db based on postId desc 4 -> 3 -> 2 -> 1 two posts of B then two posts of A like it should be.