On Sunday, December 4, 2016 at 9:00:04 PM UTC, Brian Christian wrote:
>
>
> Okay, so my issue here is:
>
> If the cache key is just based on the Posts, then the controller code will
> pull the Authors association for no reason (we don’t actually need it,
> because the author names are cached until the Post models are touched).
> This makes me think I should remove the .includes() call from my
> controller, since it will cause an unnecessary db query 99% of the time.
>
> On the other hand, if I remove the .includes() call from my controller,
> then whenever the cache *does* expire, I have an *n*-queries situation,
> which also seems bad.
>
> Is there any way to have the best of both worlds here?
>
>
The :preload variant of includes can be run after the query has run -
ActiveRecord::Associations::Preloader.new.preload(@recent, :authors)
Will load that association on @recent (you can preload multiple or nested
associations in the same way. You could do this once you've gone down the
cache miss case.
> A related question:
>
> I’ve also found it helpful to use lower-level caching in my Post model to
> cache the “recent” query like so:
>
> post.rb
> self.recent do
> Rails.cache.fetch('recent_posts’, expires_in: 1.day) do
> self.order(created_at: :desc).to_a
> end
> end
>
> Here I have a similar problem. If I don’t include the `.to_a` at the end,
> then I’m only caching the *scope*, which will still evaluate and
> seemingly (at least in development) trigger a db query on every pageview.
> If I *do* include the `.to_a` then I forfeit the ability to use
> `.includes()` in my individual controller actions or views.
>
> Again, is there a way to have the best of both worlds here?
>
>
You can use the same trick here.
Fred
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