Accessing read/unread stats via another relationship

[brendon]

Hi there, I've spent a bit of time trying to figure this out so I thought I'd ask here in case you had any pointers :)

I have a model called Values. A value has many comments, and the comments readable via your gem.

I'm rendering a document full of values so I want to select all the values in a document, and also have an additional two columns: comments_count and unread_comments_count. This allows me to render the document indicating the comments as efficiently as possible. Right now I'm issuing a query for each unread_by call that is causing a performance problem.

I've had some success getting an unread_count by merging unread_by() into the query and forcing a LEFT JOIN between values and comments. But then it doesn't seem possible to get a count of all of the comments (read and unread) in that same query.

Any pointers would be greatly appreciated. :)

[brendon]

I ended up not eager loading the comments at all (as I don't actually use the objects). Instead I'm generating a statistics hash like this:

default_hash = Hash.new { |h, k| h[k] = { unread: 0, total: 0 } }
document.comments.with_read_marks_for(current_user).reduce(default_hash) do |hash, comment|
  hash[comment.value_id][:unread] += 1 if comment.unread?(current_user)
  hash[comment.value_id][:total] += 1
  hash
end

Results in one query at the start plus several (ultimately cached) queries on the read_marks table when there are no read_marks. Works pretty well.

[ledermann]

Using with_read_marks_for is the key. It uses just one query and make sure that the following unread? invocations use the result of the first query (see code).

Your solution looks fine.

[brendon]

Thanks @ledermann, yep it's working great. Thanks for the help :)

[Frexuz]

Just stumbled upon this. @brendon's solution was exactly what we were looking for.

It would be a great addition to the README (the whole example?), and explaining that subsequent unread?(user) doesn't do an additional query. 👍

A bit unnecessary to dig through the issues / finding it by chance :)

[brendon]

Glad I was able to be of some help @Frexuz :) I'm sure @ledermann would appreciate a PR with the documentation enhancements if you had the time to do it. Would you be keen? :)

[Frexuz]

Let me give it a go :) Then @ledermann can adjust

[Frexuz]

PR here #98