Fix a N+1 query problem in the orders controller

[rymai]

The description of the problem and the fix can be found in spree/spree#9026.

Logs before:

Processing by Spree::Admin::OrdersController#index as HTML
  Spree::User Load (2.3ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 ORDER BY "spree_users"."id" ASC LIMIT $2  [["id", 96], ["LIMIT", 1]]
  Spree::Role Load (1.0ms)  SELECT "spree_roles".* FROM "spree_roles" INNER JOIN "spree_roles_users" ON "spree_roles"."id" = "spree_roles_users"."role_id" WHERE "spree_roles_users"."user_id" = $1  [["user_id", 96]]
  Rendering /Users/remy/.gem/ruby/2.5.1/gems/solidus_backend-2.6.0/app/views/spree/admin/orders/index.html.erb within spree/layouts/admin
   (1.0ms)  SELECT COUNT(*) FROM "spree_stores"
   (1.4ms)  SELECT COUNT(*) FROM "spree_orders" WHERE "spree_orders"."completed_at" IS NOT NULL
  Spree::Order Exists (0.5ms)  SELECT  1 AS one FROM "spree_orders" WHERE "spree_orders"."completed_at" IS NOT NULL LIMIT $1 OFFSET $2  [["LIMIT", 1], ["OFFSET", 0]]
  Spree::Order Load (1.5ms)  SELECT  "spree_orders".* FROM "spree_orders" WHERE "spree_orders"."completed_at" IS NOT NULL ORDER BY "spree_orders"."completed_at" DESC LIMIT $1 OFFSET $2  [["LIMIT", 15], ["OFFSET", 0]]
  Spree::User Load (0.7ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 LIMIT $2  [["id", 93], ["LIMIT", 1]]
  Spree::User Load (0.7ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 LIMIT $2  [["id", 74], ["LIMIT", 1]]
  Spree::User Load (0.7ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 LIMIT $2  [["id", 92], ["LIMIT", 1]]
  Spree::User Load (0.7ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 LIMIT $2  [["id", 90], ["LIMIT", 1]]
  CACHE Spree::User Load (0.0ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 LIMIT $2  [["id", 90], ["LIMIT", 1]]
  Spree::User Load (0.8ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 LIMIT $2  [["id", 89], ["LIMIT", 1]]
  Spree::User Load (0.8ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 LIMIT $2  [["id", 88], ["LIMIT", 1]]
  Spree::User Load (0.7ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 LIMIT $2  [["id", 87], ["LIMIT", 1]]
  Spree::User Load (0.8ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 LIMIT $2  [["id", 85], ["LIMIT", 1]]

Logs after:

Started GET "/admin/orders" for ::1 at 2018-10-05 13:55:31 +0200
Processing by Spree::Admin::OrdersController#index as HTML
  Spree::User Load (0.7ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1 ORDER BY "spree_users"."id" ASC LIMIT $2  [["id", 96], ["LIMIT", 1]]
  Spree::Role Load (0.5ms)  SELECT "spree_roles".* FROM "spree_roles" INNER JOIN "spree_roles_users" ON "spree_roles"."id" = "spree_roles_users"."role_id" WHERE "spree_roles_users"."user_id" = $1  [["user_id", 96]]
  Rendering /Users/remy/.gem/ruby/2.5.1/gems/solidus_backend-2.6.0/app/views/spree/admin/orders/index.html.erb within spree/layouts/admin
   (0.5ms)  SELECT COUNT(*) FROM "spree_stores"
   (0.6ms)  SELECT COUNT(*) FROM "spree_orders" WHERE "spree_orders"."completed_at" IS NOT NULL
  Spree::Order Exists (0.5ms)  SELECT  1 AS one FROM "spree_orders" WHERE "spree_orders"."completed_at" IS NOT NULL LIMIT $1 OFFSET $2  [["LIMIT", 1], ["OFFSET", 0]]
  Spree::Order Load (0.9ms)  SELECT  "spree_orders".* FROM "spree_orders" WHERE "spree_orders"."completed_at" IS NOT NULL ORDER BY "spree_orders"."completed_at" DESC LIMIT $1 OFFSET $2  [["LIMIT", 15], ["OFFSET", 0]]
  Spree::User Load (0.7ms)  SELECT "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" IN ($1, $2, $3, $4, $5, $6, $7, $8)  [["id", 93], ["id", 74], ["id", 92], ["id", 90], ["id", 89], ["id", 88], ["id", 87], ["id", 85]]

Fixes spree/spree#9026.

[tvdeyen]

Thanks. This is great.

Please rebase to get rid of the Netlify errors.

[rymai]

Thanks. This is great.

🎉

Please rebase to get rid of the Netlify errors.

Done, thanks!

[kennyadsl]

Thanks!

[rymai]

@kennyadsl Thanks! 🎉