Auto-increment external_account_id automatically by default to allow upcoming simple signups

app/models/account.rb

@@ -11,6 +11,7 @@ class Account < ApplicationRecord
 
   has_many_attached :uploads
 
+  before_create :assign_external_account_id
   after_create :create_join_code
 
   validates :name, presence: true
@@ -35,4 +36,9 @@ class Account < ApplicationRecord
   def system_user
     users.where(role: :system).first!
   end
+
+  private
+    def assign_external_account_id
+      self.external_account_id ||= ExternalAccount.create!.id
+    end
 end

app/models/external_account.rb

@@ -0,0 +1,5 @@
+# This is meant to provide a sequential ID for +external_account_id+ when creating
+# accounts without one. The SaaS version of the app uses that column, but most apps
+# can just go with the default handling here.
+class ExternalAccount < ApplicationRecord
+end

db/migrate/20251127000001_create_external_accounts.rb

@@ -0,0 +1,15 @@
+class CreateExternalAccounts < ActiveRecord::Migration[8.0]
+  def up
+    create_table :external_accounts do |t|
+    end
+
+    max_id = Account.maximum(:external_account_id) || 0
+    if max_id > 0
+      execute "INSERT INTO external_accounts (id) VALUES (#{max_id})"
+    end
+  end
+
+  def down
+    drop_table :external_accounts
+  end
+end

test/models/account_test.rb

@@ -59,4 +59,22 @@ class AccountTest < ActiveSupport::TestCase
       account.system_user
     end
   end
+
+  test "external_account_id auto-increments on creation" do
+    account1 = Account.create!(name: "First Account")
+    account2 = Account.create!(name: "Second Account")
+
+    assert_not_nil account1.external_account_id
+    assert_not_nil account2.external_account_id
+    assert_equal account1.external_account_id + 1, account2.external_account_id
+  end
+
+  test "external_account_id can be overridden without creating sequence entry" do
+    custom_id = Account.last.id + 99999
+
+    assert_no_difference -> { ExternalAccount.count } do
+      account = Account.create!(name: "Custom ID Account", external_account_id: custom_id)
+      assert_equal custom_id, account.external_account_id
+    end
+  end
 end