generate consecutive unique number in range - ruby-on-rails

Question

I have a field in my database to save a unique number adding the last two digits of the created_at year. At the moment it all works well, except instead of using the SecureRandom method i'm looking for an option to save consecutive numbers. ie. 1901, 1902, 1903...
Model
before_create :create_number
def create_number
loop do
self. number = ((created_at + 1.year).strftime("%y")).concat(sprintf '%02d', SecureRandom.random_number(200))
break unless self.class.exists?(:number => number)
end
end

Answer 1

The key is to use a count query fetch the count of records for that specific year:
class Thing < ApplicationRecord
before_commit :create_number!, if: -> { number.nil? }
private
def count_records_from_same_year
self.class.where(
created_at: (created_at.beginning_of_year..created_at.end_of_year)
).count
end
def create_number!
loop do
year = (created_at + 1.year).strftime("%y")
self.number = year.concat(sprintf '%02d', count_records_from_same_year)
break unless self.class.where(number: self.number).exists?
end
end
end
As you can see it generates consecutive numbers:
irb(main):001:0> Thing.create
(0.3ms) BEGIN
Thing Create (1.3ms) INSERT INTO "things" ("created_at", "updated_at") VALUES ($1, $2) RETURNING "id" [["created_at", "2018-10-12 09:57:24.527527"], ["updated_at", "2018-10-12 09:57:24.527527"]]
(1.2ms) SELECT COUNT(*) FROM "things" WHERE "things"."created_at" BETWEEN $1 AND $2 [["created_at", "2018-01-01 00:00:00"], ["created_at", "2018-12-31 23:59:59.999999"]]
Thing Exists (1.4ms) SELECT 1 AS one FROM "things" WHERE "things"."number" = $1 LIMIT $2 [["number", "1901"], ["LIMIT", 1]]
(0.7ms) COMMIT
=> #<Thing id: 1, number: "1901", created_at: "2018-10-12 09:57:24", updated_at: "2018-10-12 09:57:24">
irb(main):002:0> Thing.create
(0.3ms) BEGIN
Thing Create (0.8ms) INSERT INTO "things" ("created_at", "updated_at") VALUES ($1, $2) RETURNING "id" [["created_at", "2018-10-12 09:57:26.402797"], ["updated_at", "2018-10-12 09:57:26.402797"]]
(0.7ms) SELECT COUNT(*) FROM "things" WHERE "things"."created_at" BETWEEN $1 AND $2 [["created_at", "2018-01-01 00:00:00"], ["created_at", "2018-12-31 23:59:59.999999"]]
Thing Exists (0.8ms) SELECT 1 AS one FROM "things" WHERE "things"."number" = $1 LIMIT $2 [["number", "1902"], ["LIMIT", 1]]
(0.7ms) COMMIT
=> #<Thing id: 2, number: "1902", created_at: "2018-10-12 09:57:26", updated_at: "2018-10-12 09:57:26">
irb(main):003:0> Thing.create
(0.5ms) BEGIN
Thing Create (0.7ms) INSERT INTO "things" ("created_at", "updated_at") VALUES ($1, $2) RETURNING "id" [["created_at", "2018-10-12 09:57:27.537635"], ["updated_at", "2018-10-12 09:57:27.537635"]]
(1.6ms) SELECT COUNT(*) FROM "things" WHERE "things"."created_at" BETWEEN $1 AND $2 [["created_at", "2018-01-01 00:00:00"], ["created_at", "2018-12-31 23:59:59.999999"]]
Thing Exists (0.6ms) SELECT 1 AS one FROM "things" WHERE "things"."number" = $1 LIMIT $2 [["number", "1903"], ["LIMIT", 1]]
(0.7ms) COMMIT
=> #<Thing id: 3, number: "1903", created_at: "2018-10-12 09:57:27", updated_at: "2018-10-12 09:57:27">