Add Determine The Configured Primary Key Type as a Rails TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1582 TILs and counting..._
+_1583 TILs and counting..._
 
 See some of the other learning resources I work on:
 - [Ruby Operator Lookup](https://www.visualmode.dev/ruby-operators)
@@ -993,6 +993,7 @@ See some of the other learning resources I work on:
 - [Define The Root Path For The App](rails/define-the-root-path-for-the-app.md)
 - [Delete Paranoid Records](rails/delete-paranoid-records.md)
 - [Demodulize A Class Name](rails/demodulize-a-class-name.md)
+- [Determine The Configured Primary Key Type](rails/determine-the-configured-primary-key-type.md)
 - [Different Ways To Add A Foreign Key Reference](rails/different-ways-to-add-a-foreign-key-reference.md)
 - [Disambiguate Where In A Joined Relation](rails/disambiguate-where-in-a-joined-relation.md)
 - [Empty find_by Returns First Record](rails/empty-find-by-returns-first-record.md)

rails/determine-the-configured-primary-key-type.md

@@ -0,0 +1,35 @@
+# Determine The Configured Primary Key Type
+
+I noticed an interesting helper function in the database migration generated by
+`bin/rails active_storage:install`.
+
+```ruby
+class CreateActiveStorageTables < ActiveRecord::Migration[8.0]
+  def change
+    # Use Active Record's configured type for primary and foreign keys
+    primary_key_type, foreign_key_type = primary_and_foreign_key_types
+
+    # ...
+  end
+
+  private
+
+    def primary_and_foreign_key_types
+      config = Rails.configuration.generators
+      setting = config.options[config.orm][:primary_key_type]
+      primary_key_type = setting || :primary_key
+      foreign_key_type = setting || :bigint
+      [ primary_key_type, foreign_key_type ]
+    end
+end
+```
+
+The `primary_and_foreign_key_types` method looks in the generators config for
+the ORM (`:active_record`) to determine the configured `:primary_key_type`. By
+default this will return `nil`. This method then uses `:primary_key` as a
+fallback value which will be `bigint`. That's why the `foreign_key_type` falls
+back to `:bigint`.
+
+If desired, this can be manually configured in `config/application.rb` like
+shown in the [ActiveRecord Migrations
+docs](https://guides.rubyonrails.org/active_record_migrations.html#enabling-uuids-in-rails).