Rails：通过关联预载has_many

Question

I have a Trailer model and each Trailer belongs_to a Movie, and a Movie has_many :releases. And Trailer has_many :releases through :movie

Release has a column :medium which can be "Netflix", "Theater", or "Torrent".

In my controller:

@trailers = Trailer.all

In my view, I want to check the releases of each trailer:

<%= render @trailers %>

then:

if trailer.releases.where(medium:"Torrent").first
  # show a Torrent icon
end

Is there a way to preload trailer.releases so that I'm not hammering the DB and calling trailer.releases.where(medium:"Torrent").first, trailer.releases.where(medium:"Netflix").first, trailer.releases.where(medium:"Theater").first for each trailer that gets rendered?

How do I optimize this?

Answer 1

Try in controller:

@trailers = Trailer.all # 1 query to DB
@movies_releases = %w(Torrent Netflix Theater).map do |medium|
  [medium, Release.where(medium: medium).pluck('DISTINCT movie_id')]
end.to_h # 3 queries to DB

And then in view:

if @movies_releases['Torrent'].include?(trailer.movie_id)
  # show a Torrent icon
end