Exposing primary keys externally just sort of invites people to poke around in your system. Lets configure rails to use uuid instead.

Create a postgres rails app

We are going to be relying upon the pgcrypto postgres extension, so lets go ahead a create a postgres based rails application.

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rails new testapp -d=postgresql
cd testapp

Now we tell our generators that we want our primary key type to be :uuid:

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# config/initializers/generators.rb
Rails.application.config.generators do |g|
  g.orm :active_record, primary_key_type: :uuid
end

And we need to change the sort order, since when using integer id's for the primary key rails uses that. We'll tell it to use created_at instead:

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# app/models/application_record.rb
class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
  # Sort records by date of creation instead of primary key
  self.implicit_order_column = :created_at
end

Create your first migration

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rails g model post title content:text

And make sure that we add to the change method of the migration!

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enable_extension 'pgcrypto' unless extension_enabled?('pgcrypto')

Start postgres and test it out

Lets create a throwaway postgres container to see how things are working

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docker run -it --rm -p 5432:5432 -e POSTGRES_PASSWORD=password postgres:13.1

This will delete itself when you close out of it.

We'll need to create a simple config/database.yml file to connect to it:

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default: &default
  adapter: postgresql
  encoding: unicode
  host: localhost
  username: postgres
  password: password
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: testapp_development

test:
  <<: *default
  database: testapp_test

production:
  <<: *default
  database: testapp_production

And then we create and migrate:

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rake db:create:all
rake db:migrate

And now we can test it out:

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$ rails c
Running via Spring preloader in process 3134
Loading development environment (Rails 6.0.3.4)
irb(main):001:0> Post.create title: "First post"
   (0.5ms)  BEGIN
  Post Create (3.5ms)  INSERT INTO "posts" ("title", "created_at", "updated_at") VALUES ($1, $2, $3) RETURNING "id"  [["title", "First post"], ["created_at", "2020-11-22 16:36:20.826249"], ["updated_at", "2020-11-22 16:36:20.826249"]]
   (8.7ms)  COMMIT
=> #<Post id: "4c3f20d0-a17b-473d-99f1-9824ba5207c2", title: "First post", content: nil, created_at: "2020-11-22 16:36:20", updated_at: "2020-11-22 16:36:20">
irb(main):002:0> Post.create title: "Second post"
   (3.1ms)  BEGIN
  Post Create (13.0ms)  INSERT INTO "posts" ("title", "created_at", "updated_at") VALUES ($1, $2, $3) RETURNING "id"  [["title", "Second post"], ["created_at", "2020-11-22 16:36:27.499092"], ["updated_at", "2020-11-22 16:36:27.499092"]]
   (26.5ms)  COMMIT
=> #<Post id: "2c1da815-dfe4-48e5-bdb7-13a573035825", title: "Second post", content: nil, created_at: "2020-11-22 16:36:27", updated_at: "2020-11-22 16:36:27">
irb(main):003:0> Post.last
  Post Load (0.7ms)  SELECT "posts".* FROM "posts" ORDER BY "posts"."created_at" DESC LIMIT $1  [["LIMIT", 1]]
=> #<Post id: "2c1da815-dfe4-48e5-bdb7-13a573035825", title: "Second post", content: nil, created_at: "2020-11-22 16:36:27", updated_at: "2020-11-22 16:36:27">

The sql for the Post.last command is SELECT "posts".* FROM "posts" ORDER BY "posts"."created_at" DESC LIMIT $1 which is using the created_at column.

But this doesn't support sqlite

The uuid column type isn't supported by sqlite. I think it's better to test on the same database type as production, and with docker it's easy to throw things up and tear them down, etc. but caveat.