Fetch with includes

1.rb

[2] pry(main)> Product.last(10).map{|p| p.variants}.flatten
  Product Load (1.1ms)  SELECT  "products".* FROM "products"  ORDER BY "products"."id" DESC LIMIT 10
  Variant Load (96.5ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247664 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247664]]
  Variant Load (0.6ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247665 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247665]]
  Variant Load (0.3ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247666 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247666]]
  Variant Load (0.6ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247667 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247667]]
  Variant Load (0.5ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247668 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247668]]
  Variant Load (0.5ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247670 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247670]]
  Variant Load (0.5ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247675 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247675]]
  Variant Load (0.9ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247676 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247676]]
  Variant Load (0.6ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247677 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247677]]
  Variant Load (0.5ms)  SELECT "variants".* FROM "variants" WHERE "variants"."nomenclature_id" = 247678 AND "variants"."archived_at" IS NULL  ORDER BY order_weight  [["nomenclature_id", 247678]]
=> [#<Variant:0x00000004c4bc20
 #<Variant:0x0000000457db00
 #<Variant:0x0000000366ae38 ...


[3] pry(main)> Product.includes(:variants).last(10).map{|p| p.variants}.flatten
  Product Load (1.0ms)  SELECT  "products".* FROM "products"  ORDER BY "products"."id" DESC LIMIT 10
  Variant Load (1.3ms)  SELECT "variants".* FROM "variants" WHERE "variants"."archived_at" IS NULL AND "variants"."nomenclature_id" IN (247678, 247677, 247676, 247675, 247670, 247668, 247667, 247666, 247665, 247664)  ORDER BY order_weight
=> [#<Variant:0x000000097f5130
 #<Variant:0x000000097f4ff0
 #<Variant:0x000000097f4eb0