Mysterious entries in topic_users table

Contribute Bug
10

I’ve been looking at topic_users a bit lately.

I was confused as to why there would be these two fields

last_read_post_number    integer    null 
highest_seen_post_number    integer    null

I mean, if I read it, I saw it, no?

Then I found this in app/models/topic_user.rb

      # In case anyone seens "highest_seen_post_number" and gets confused, like I do.
      # highest_seen_post_number represents the highest_post_number of the topic when
      # the user visited it. It may be out of alignment with last_read, meaning
      # ... user visited the topic but did not read the posts

In other words, if a topic has 100 posts, but I only read the first 50, the two will not be the same.

I just ran

SELECT *
FROM topic_users
WHERE last_read_post_number IS NULL 
OR  highest_seen_post_number IS NULL

In all results both read and seen were NULL
and I noticed in all results total_msecs_viewed was zero.

In some, it was not the topic id that was used, but the post id

topic-users-null.png635×387 17.9 KB

My guess, without having looked more closely into the code yet, is that there is a “divide by 0” error happening somewhere.

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