This proved a little trickier, but the result is actually pretty dang cool. I’m not quite done implementing this yet but I’m confident it can be done.

To take your example a little further: Let’s say you were implementing user search. In the results, you wanted to display the user’s last thread, the first post in that thread, and user’s latest post in any thread.

Normal users can’t see banned users or archived threads or posts, but moderators can see both.

Here’s how it might look like using Janus:

latest_thread = Thread |> order_by(desc: :inserted_at) |> limit(1)
first_post = Post |> where(index: 0) |> limit(1)
latest_post = Post |> order_by(desc: :inserted_at) |> limit(1)

search_params
|> Accounts.search()
|> Policy.filter(:read, current_user,
  preload_filtered: [
    threads: {latest_thread, posts: first_post},
    posts: latest_post
  ]
)
|> Repo.all()

The result of this would be the users that the current user can read, preloaded with the latest thread created by that user (and that thread’s first post) that the current user can read, and the latest post by that user that the current user can read. So a normal user would see non-banned users and non-archived threads/posts, while a moderator may see banned users and archived threads/posts mixed into the results. This all done with a single query and includes users that may have no threads or posts.

Man, Ecto is really cool.