Fix enum serialization in rails 4.2

Fixes #798

Our test suite has one model that tests enums, PostWithStatus. Its
spec did not cover `touch_with_version`. Somehow, probably during
our upgrade to rails 5, we broke `touch_with_version` for enums.
Unlike other methods, when an enum arrives at
`CastAttributeSerializer#serialize` during `touch_with_version`, it
is already a number. We assumed it was always a string.

This is sort of a hack, just handling both strings and numbers in
`#serialize`. I'd rather figure out how a number got to `#serialize`
in the first place. However, a hack is acceptable, as it's only
for rails 4.2, and the hack will eventually be deleted when we
drop support for 4.2.

CHANGELOG.md

@@ -14,7 +14,9 @@
 
 ### Fixed
 
-- None
+- [#798](https://github.com/airblade/paper_trail/issues/798) -
+  Fix a rare bug with serialization of enums in rails 4.2 only when
+  using `touch_with_version`.
 
 ## 5.2.0 (2016-06-27)
 

lib/paper_trail/attribute_serializers/cast_attribute_serializer.rb

@@ -34,8 +34,13 @@ module PaperTrail
         end
 
         def serialize(attr, val)
-          val = defined_enums[attr][val] if defined_enums[attr]
-          @klass.type_for_attribute(attr).type_cast_for_database(val)
+          castable_val = val
+          if defined_enums[attr]
+            # `attr` is an enum. Find the number that corresponds to `val`. If `val` is
+            # a number already, there won't be a corresponding entry, just use `val`.
+            castable_val = defined_enums[attr][val] || val
+          end
+          @klass.type_for_attribute(attr).type_cast_for_database(castable_val)
         end
 
         def deserialize(attr, val)
@@ -49,6 +54,8 @@ module PaperTrail
 
         private
 
+        # ActiveRecord::Enum was added in AR 4.1
+        # http://edgeguides.rubyonrails.org/4_1_release_notes.html#active-record-enums
         def defined_enums
           @defined_enums ||= (@klass.respond_to?(:defined_enums) ? @klass.defined_enums : {})
         end

spec/models/post_with_status_spec.rb

@@ -1,7 +1,7 @@
 require "rails_helper"
 
-# This model is in the test suite soley for the purpose of testing ActiveRecord::Enum,
-# which is available in ActiveRecord4+ only
+# This model tests ActiveRecord::Enum, which was added in AR 4.1
+# http://edgeguides.rubyonrails.org/4_1_release_notes.html#active-record-enums
 describe PostWithStatus, type: :model do
   if defined?(ActiveRecord::Enum)
     with_versioning do
@@ -22,6 +22,19 @@ describe PostWithStatus, type: :model do
           expect(subject.changeset["status"]).to eql %w(published archived)
         end
       end
+
+      describe "#touch_with_version" do
+        it "preserves the enum value (and all other attributes)" do
+          post = described_class.create(status: :draft)
+          expect(post.versions.count).to eq(1)
+          expect(post.status).to eq("draft")
+          Timecop.travel 1.second.since # because MySQL lacks fractional seconds precision
+          post.paper_trail.touch_with_version
+          expect(post.versions.count).to eq(2)
+          expect(post.versions.last[:object]).to include("status: 0")
+          expect(post.paper_trail.previous_version.status).to eq("draft")
+        end
+      end
     end
   end
 end