From https://once.com/writebook

app/models/account/joinable.rb

@@ -0,0 +1,16 @@
+module Account::Joinable
+  extend ActiveSupport::Concern
+
+  included do
+    before_create { self.join_code = generate_join_code }
+  end
+
+  def reset_join_code
+    update! join_code: generate_join_code
+  end
+
+  private
+    def generate_join_code
+      SecureRandom.alphanumeric(12).scan(/.{4}/).join("-")
+    end
+end