Rails 4 Eager load limit subquery -

is there way avoid n+1 problem when eager loading , applying limit subquery? want avoid lots of sql queries this:

category.all.each |category|   category.posts.limit(10) end 

but want 10 posts per category, standard eager loading, gets posts, not suffice:

category.includes(:posts).all 

what best way solve problem? n+1 way limit amount of posts per category?

from rails docs

if eager load association specified :limit option, ignored, returning associated objects

so given following model definition

class category < activerecord::base   has_many :posts   has_many :included_posts, -> { limit 10 }, class_name: "post" end 

calling category.find(1).included_posts work expected , apply limit of 10 in query. however, if try category.includes(:included_posts).all limit option ignored. can see why case if @ sql generated eager load

category.includes(:posts).all  category load (0.2ms)  select "categories".* "categories" post load (0.4ms)  select "posts".* "posts" "posts"."category_id" in (1, 2, 3) 

if added limit clause posts query, return total of 10 posts , not 10 posts per category might expect.

getting problem, eager load posts , limit loaded collection using first(10)

categories = category.includes(:posts).all categories.first.posts.first(10) 

although you're loading more models memory, bound more performant since you're making 2 calls against database vs. n+1. cheers.