Why are IDs specified via <%= ActiveRecord::FixtureSet.identify("david", :uuid) %>

Taken from Fizzy (publicly available).

# users.yml
david:
  id: <%= ActiveRecord::FixtureSet.identify("david", :uuid) %>
  name: David
  role: member
  identity: david
  account: 37s_uuid  # <------ notice this here
  verified_at: <%= Time.current.to_fs(:db) %>

Source: https://github.com/basecamp/fizzy/blob/main/test/fixtures/users.yml

Notice the key-value entry for account?

# Let's review the accounts.yml file
37s:
  id: <%= ActiveRecord::FixtureSet.identify("37s", :uuid) %>  # < ---- check this out
  name: 37signals
  external_account_id: <%= ActiveRecord::FixtureSet.identify("37signals") %>
  cards_count: 5

Source: https://github.com/basecamp/fizzy/blob/main/test/fixtures/accounts.yml

Notice how you can reference IDs via name e.g. via 37s_uuid without using a label?

Label Names

Checkout out the section: “Stable, Autogenerated IDs” in the following link: https://api.rubyonrails.org/v8.0.1/classes/ActiveRecord/FixtureSet.html

You can definitely use label names: instead of specifying IDs like this: <%= ActiveRecord::FixtureSet.identify("37s", :uuid) %> - but if you want a UUID - something that is absolutely unique no matter what, then you will have to use the ruby code just mentioned. That will give you a compliant UUID, whereas a label will not give you that. If you are ok with labels, the following will be fine:

From the docs:

Here, have a monkey fixture:

george:
  id: 1
  name: George the Monkey

reginald:
  id: 2
  name: Reginald the Pirate

Each of these fixtures has two unique identifiers: one for the database and one for the humans. Why don’t we generate the primary key instead? Hashing each fixture’s label yields a consistent ID:

george: # generated id: 503576764
  name: George the Monkey

reginald: # generated id: 324201669
  name: Reginald the Pirate