Rails eager loading and kaminari

Question

How to use eager loading while paginating with kaminari? I know that kaminari needs Relation object to work, how to retrieve models with :include and return Relation object?
And second question, why :include creates sql query for evry defined model instead of creating one big joined query?

# match.rb
class Match < ActiveRecord::Base
  has_many :rounds
  has_many :participations
  has_many :players, :through => :participations
  has_many :scores
  has_many :clans, :through => :scores
  belongs_to :clan_1, :class_name => "Clan", :foreign_key => "clan_1_id"
  belongs_to :clan_2, :class_name => "Clan", :foreign_key => "clan_2_id"
  belongs_to :winner, :class_name => "Clan", :foreign_key => "winner_id"
  belongs_to :league
  belongs_to :tournament

# matches_controller.rb
@matches = Match.all(:include=>[:clans,:scores])

This is what log outputs for Match.includes(:clans):

Match Load (18.2ms)  SELECT "matches".* FROM "matches"
Score Load (4.5ms)  SELECT "scores".* FROM "scores" WHERE ("scores".match_id IN (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115))
Clan Load (0.5ms)  SELECT "clans".* FROM "clans" WHERE ("clans"."id" IN (1,7,9,2,5,3,4,8,10,6,11,12,13,14,15,16,17,18,19,20))

I think you should try to use new Rails ActiveRecors chain query syntax — fl00r, Mar 26 '11 at 19:20

score 2 · Accepted Answer · answered Mar 26 '11 at 19:19

2

In Rails 3.x there is new query syntax. So try this

@matches = Match.includes(:clans,:scores)

answered Mar 26 '11 at 19:19

fl00r

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Much better because it returns `Relation` object but still generating 3 queries for `Match.includes(:clans). Updated question with queries, take a look. – methyl Mar 26 '11 at 19:32
But, view rendering time increases from 20 to 150ms when change from all(:include) to .includes() – methyl Mar 26 '11 at 20:11

score 0 · Answer 2 · answered Aug 30 '13 at 09:31

Try this:

@matches = Match.includes([:clans,:scores]).all()
@matches_paginated = Kaminari.paginate_array(@matches).page(params[:page] || 1).per(20)

# And then
@matches_paginated.each do |m|
  m.clans.each do |c| # should not generate a new query
    c.name # should not generate a new query
  end
end

The only problem with this is that this will eager load all the other pages (which you really don't need)

Rails eager loading and kaminari

2 Answers2