How to eager load association for an array of model records

Question

I have an array of Rails model records. Is it possible to eager load an association for all these records in one go (query)?

Sometimes I only have an array instead of an AR::Scope. And sometimes I want to dynamically choose what to eager load later.

score 36 · Accepted Answer · edited Feb 02 '16 at 11:38

36

In Rails 3, one can use preloader to eager-load associations on existing records.

ActiveRecord::Associations::Preloader.new(posts,:comments).run()

In Rails 4.1+ the call signature changed slightly:

ActiveRecord::Associations::Preloader.new.preload(posts,:comments)

edited Feb 02 '16 at 11:38

NobodysNightmare

answered Mar 12 '13 at 09:52

lulalala

2

This is deprecated in Rails 4.2 – Leo Correa Nov 17 '15 at 18:21
3

Rails4: `ActiveRecord::Associations::Preloader.new.preload(posts, :catalogs)` – Hooopo Nov 24 '15 at 18:08
@LeoCorrea I don't see it's deprecated in Rails 4.2. Can you give some hint where I can find the deprecation note? Thanks. – Anh Nguyen Apr 15 '16 at 20:53
2

`ActiveRecord::Associations::Preloader.new.preload(posts,:comments)` still works in Rails 5! – Finn Oct 21 '18 at 23:32

score 1 · Answer 2 · answered Sep 24 '12 at 09:58

1

Well, you could refind those objects. Map ':id' over your array, to get the records' ids, and then refind, this time eager-loading.

If your array of, say, Post model records is posts, then it'd be:

Post.find(posts.map &:id).includes(:blah)

answered Sep 24 '12 at 09:58

Gabe Durazo

1

My set is quite large so this reloading is too expensive. I was hoping for an API way. – lulalala Sep 25 '12 at 01:33

2 Answers2