Fix deserialization of enums written by PT 4

CHANGELOG.md

@@ -14,6 +14,8 @@
 
 ### Fixed
 
+- [#857](https://github.com/airblade/paper_trail/pull/857) -
+  Fix deserialization of enums written by PT 4.
 - [#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`.

lib/paper_trail/attribute_serializers/cast_attribute_serializer.rb

@@ -8,19 +8,41 @@ module AttributeSerializers
     # This implementation depends on the `type_for_attribute` method, which was
     # introduced in rails 4.2. In older versions of rails, we shim this method
     # with `LegacyActiveRecordShim`.
+    class CastAttributeSerializer
+      def initialize(klass)
+        @klass = klass
+      end
+
+      private
+
+      # Returns a hash mapping attributes to hashes that map strings to
+      # integers. Example:
+      #
+      # ```
+      # { "status" => { "draft"=>0, "published"=>1, "archived"=>2 } }
+      # ```
+      #
+      # 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
+    end
+
     if ::ActiveRecord::VERSION::MAJOR >= 5
       # This implementation uses AR 5's `serialize` and `deserialize`.
       class CastAttributeSerializer
-        def initialize(klass)
-          @klass = klass
-        end
-
         def serialize(attr, val)
           @klass.type_for_attribute(attr).serialize(val)
         end
 
         def deserialize(attr, val)
-          @klass.type_for_attribute(attr).deserialize(val)
+          if defined_enums[attr] && val.is_a?(::String)
+            # Because PT 4 used to save the string version of enums to `object_changes`
+            val
+          else
+            @klass.type_for_attribute(attr).deserialize(val)
+          end
         end
       end
     else
@@ -29,10 +51,6 @@ def deserialize(attr, val)
       # `type_cast_for_database` in our shim attribute type classes,
       # `NoOpAttribute` and `SerializedAttribute`.
       class CastAttributeSerializer
-        def initialize(klass)
-          @klass = klass
-        end
-
         def serialize(attr, val)
           castable_val = val
           if defined_enums[attr]
@@ -44,21 +62,18 @@ def serialize(attr, val)
         end
 
         def deserialize(attr, val)
-          val = @klass.type_for_attribute(attr).type_cast_from_database(val)
-          if defined_enums[attr]
-            defined_enums[attr].key(val)
-          else
+          if defined_enums[attr] && val.is_a?(::String)
+            # Because PT 4 used to save the string version of enums to `object_changes`
             val
+          else
+            val = @klass.type_for_attribute(attr).type_cast_from_database(val)
+            if defined_enums[attr]
+              defined_enums[attr].key(val)
+            else
+              val
+            end
           end
         end
-
-        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
       end
     end
   end

spec/models/post_with_status_spec.rb

@@ -5,14 +5,24 @@
 describe PostWithStatus, type: :model do
   if defined?(ActiveRecord::Enum)
     with_versioning do
-      let(:post) { PostWithStatus.create!(status: "draft") }
+      let(:post) { described_class.create!(status: "draft") }
 
       it "should stash the enum value properly in versions" do
         post.published!
         post.archived!
         expect(post.paper_trail.previous_version.published?).to be true
       end
 
+      it "can read enums in version records written by PT 4" do
+        post = described_class.create(status: "draft")
+        post.published!
+        version = post.versions.last
+        # Simulate behavior PT 4, which used to save the string version of
+        # enums to `object_changes`
+        version.update(object_changes: "---\nid:\n- \n- 1\nstatus:\n- draft\n- published\n")
+        assert_equal %w(draft published), version.changeset["status"]
+      end
+
       context "storing enum object_changes" do
         subject { post.versions.last }