Do not allow multiple has_paper_trail definitions for models

CHANGELOG.md

@@ -7,7 +7,10 @@ recommendations of [keepachangelog.com](http://keepachangelog.com/).
 
 ### Breaking Changes
 
-- None
+- [#1478](https://github.com/paper-trail-gem/paper_trail/issues/1478) Do not allow
+  multiple `has_paper_trail` definitions for models. Previously, when `has_paper_trail`
+  was called on a parent and a child from STI, then possibly multiple `version` records
+  will be created per event (`create`, `destroy` etc).
 
 ### Added
 

lib/paper_trail/has_paper_trail.rb

@@ -68,6 +68,8 @@ module ClassMethods
       #
       # @api public
       def has_paper_trail(options = {})
+        raise Error, "has_paper_trail must be called only once" if self < InstanceMethods
+
         defaults = PaperTrail.config.has_paper_trail_defaults
         paper_trail.setup(defaults.merge(options))
       end

spec/dummy_app/app/models/callback_modifier.rb

@@ -1,7 +1,11 @@
 # frozen_string_literal: true
 
-class CallbackModifier < ApplicationRecord
-  has_paper_trail on: []
+module CallbackModifier
+  extend ActiveSupport::Concern
+
+  included do
+    self.table_name = "callback_modifiers"
+  end
 
   def test_destroy
     transaction do
@@ -17,33 +21,45 @@ def flagged_deleted?
   end
 end
 
-class BeforeDestroyModifier < CallbackModifier
+class BeforeDestroyModifier < ApplicationRecord
+  include CallbackModifier
+
   has_paper_trail on: []
   paper_trail.on_destroy :before
 end
 
 unless ActiveRecord::Base.belongs_to_required_by_default
-  class AfterDestroyModifier < CallbackModifier
+  class AfterDestroyModifier < ApplicationRecord
+    include CallbackModifier
+
     has_paper_trail on: []
     paper_trail.on_destroy :after
   end
 end
 
-class NoArgDestroyModifier < CallbackModifier
+class NoArgDestroyModifier < ApplicationRecord
+  include CallbackModifier
+
   has_paper_trail on: []
   paper_trail.on_destroy
 end
 
-class UpdateModifier < CallbackModifier
+class UpdateModifier < ApplicationRecord
+  include CallbackModifier
+
   has_paper_trail on: []
   paper_trail.on_update
 end
 
-class CreateModifier < CallbackModifier
+class CreateModifier < ApplicationRecord
+  include CallbackModifier
+
   has_paper_trail on: []
   paper_trail.on_create
 end
 
-class DefaultModifier < CallbackModifier
+class DefaultModifier < ApplicationRecord
+  include CallbackModifier
+
   has_paper_trail
 end

spec/paper_trail/model_config_spec.rb

@@ -5,6 +5,16 @@
 module PaperTrail
   ::RSpec.describe ModelConfig do
     describe "has_paper_trail" do
+      it "raises when called multiple times" do
+        klass = Class.new(ApplicationRecord) do
+          has_paper_trail
+        end
+
+        expect do
+          klass.has_paper_trail
+        end.to raise_error(Error, "has_paper_trail must be called only once")
+      end
+
       describe "versions:" do
         it "name can be passed instead of an options hash", :deprecated do
           allow(::ActiveSupport::Deprecation).to receive(:warn)