* Converts queries to use active record instead of raw sql. This ensures
that user objects are loaded by rails in the join, so that we
don't have to issue `User.find` calls to load users one-by-one.
* Use `.includes` to preload associations used in the view, to avoid
additional N+1 query problems (primarily, calls to link_to_user
also causing users to be loaded one-by-one).
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