Support for reifying belongs_to relationships

README.md

@@ -746,7 +746,8 @@ the association that are created in the same transaction.
 
 To restore Has-One associations as they were at the time, pass option `:has_one
 => true` to `reify`. To restore Has-Many and Has-Many-Through associations, use
-option `:has_many => true`.  For example:
+option `:has_many => true`. To restore Belongs-To association, use
+option `:belongs_to => true`. For example:
 
 ```ruby
 class Location < ActiveRecord::Base

lib/paper_trail/reifier.rb

@@ -13,6 +13,7 @@ def reify(version, options)
           mark_for_destruction: false,
           has_one: false,
           has_many: false,
+          belongs_to: false,
           unversioned_attributes: :nil
         )
 
@@ -60,15 +61,6 @@ def reify(version, options)
 
       private
 
-      def reify_associations(model, options, version)
-        if options[:has_one]
-          reify_has_ones version.transaction_id, model, options
-        end
-        if options[:has_many]
-          reify_has_manys version.transaction_id, model, options
-        end
-      end
-
       # Set all the attributes in this version on the model.
       def reify_attributes(model, version, attrs)
         enums = model.class.respond_to?(:defined_enums) ? model.class.defined_enums : {}
@@ -114,7 +106,7 @@ def prepare_array_for_has_many(array, options, versions)
           elsif version.event == "create"
             options[:mark_for_destruction] ? record.tap(&:mark_for_destruction) : nil
           else
-            version.reify(options.merge(has_many: false, has_one: false))
+            version.reify(options.merge(has_many: false, has_one: false, belongs_to: false))
           end
         end
 
@@ -123,7 +115,7 @@ def prepare_array_for_has_many(array, options, versions)
         # associations.
         array.concat(
           versions.values.map { |v|
-            v.reify(options.merge(has_many: false, has_one: false))
+            v.reify(options.merge(has_many: false, has_one: false, belongs_to: false))
           }
         )
 
@@ -132,6 +124,14 @@ def prepare_array_for_has_many(array, options, versions)
         nil
       end
 
+      def reify_associations(model, options, version)
+        reify_has_ones version.transaction_id, model, options if options[:has_one]
+
+        reify_belongs_tos version.transaction_id, model, options if options[:belongs_to]
+
+        reify_has_manys version.transaction_id, model, options if options[:has_many]
+      end
+
       # Restore the `model`'s has_one associations as they were when this
       # version was superseded by the next (because that's what the user was
       # looking at when they made the change).
@@ -156,7 +156,7 @@ def reify_has_ones(transaction_id, model, options = {})
               end
             end
           else
-            child = version.reify(options.merge(has_many: false, has_one: false))
+            child = version.reify(options.merge(has_many: false, has_one: false, belongs_to: false))
             model.appear_as_new_record do
               without_persisting(child) do
                 model.send "#{assoc.name}=", child
@@ -166,6 +166,30 @@ def reify_has_ones(transaction_id, model, options = {})
         end
       end
 
+      def reify_belongs_tos(transaction_id, model, options = {})
+        associations = model.class.reflect_on_all_associations(:belongs_to)
+
+        associations.each do |assoc|
+          next unless assoc.klass.paper_trail_enabled_for_model?
+          collection_key = model.send(assoc.association_foreign_key)
+
+          version = assoc.klass.paper_trail_version_class.
+            where("item_type = ?", assoc.class_name).
+            where("item_id = ?", collection_key).
+            where("created_at >= ? OR transaction_id = ?", options[:version_at], transaction_id).
+            order("id").limit(1).first
+
+          collection = if version.nil?
+                         assoc.klass.where(assoc.klass.primary_key => collection_key).first
+                       else
+                         version.reify(options.merge(has_many: false, has_one: false,
+                                                     belongs_to: false))
+                       end
+
+          model.send("#{assoc.name}=".to_sym, collection)
+        end
+      end
+
       # Restore the `model`'s has_many associations as they were at version_at
       # timestamp We lookup the first child versions after version_at timestamp or
       # in same transaction.

test/unit/associations_test.rb

@@ -769,4 +769,126 @@ class AssociationsTest < ActiveSupport::TestCase
       end
     end
   end
+
+  context "belongs_to associations" do
+    context "Wotsit and Widget" do
+      setup { @widget = Widget.create(name: "widget_0") }
+
+      context "where the association is created between model versions" do
+        setup do
+          @wotsit = Wotsit.create(name: "wotsit_0")
+          Timecop.travel 1.second.since
+          @wotsit.update_attributes widget_id: @widget.id, name: "wotsit_1"
+        end
+
+        context "when reified" do
+          setup { @wotsit_0 = @wotsit.versions.last.reify(belongs_to: true) }
+
+          should "see the associated as it was at the time" do
+            assert_equal nil, @wotsit_0.widget
+          end
+
+          should "not persist changes to the live association" do
+            assert_equal @widget, @wotsit.reload.widget
+          end
+        end
+
+        context "and then the associated is updated between model versions" do
+          setup do
+            @widget.update_attributes name: "widget_1"
+            @widget.update_attributes name: "widget_2"
+            Timecop.travel 1.second.since
+            @wotsit.update_attributes name: "wotsit_2"
+            @widget.update_attributes name: "widget_3"
+          end
+
+          context "when reified" do
+            setup { @wotsit_1 = @wotsit.versions.last.reify(belongs_to: true) }
+
+            should "see the associated as it was at the time" do
+              assert_equal "widget_2", @wotsit_1.widget.name
+            end
+
+            should "not persist changes to the live association" do
+              assert_equal "widget_3", @wotsit.reload.widget.name
+            end
+          end
+
+          context "when reified opting out of belongs_to reification" do
+            setup { @wotsit_1 = @wotsit.versions.last.reify(belongs_to: false) }
+
+            should "see the associated as it is live" do
+              assert_equal "widget_3", @wotsit_1.widget.name
+            end
+          end
+        end
+
+        context "and then the associated is destroyed" do
+          setup do
+            @wotsit.update_attributes name: "wotsit_2"
+            @widget.destroy
+          end
+
+          context "when reified" do
+            setup { @wotsit_2 = @wotsit.versions.last.reify(belongs_to: true) }
+
+            should "see the associated as it was at the time" do
+              assert_equal @widget, @wotsit_2.widget
+            end
+
+            should "not persist changes to the live association" do
+              assert_nil @wotsit.reload.widget
+            end
+          end
+
+          context "and then the model is updated" do
+            setup do
+              Timecop.travel 1.second.since
+              @wotsit.update_attributes name: "wotsit_3"
+            end
+
+            context "when reified" do
+              setup { @wotsit_2 = @wotsit.versions.last.reify(belongs_to: true) }
+
+              should "see the associated as it was the time" do
+                assert_nil @wotsit_2.widget
+              end
+            end
+          end
+        end
+      end
+
+      context "where the association is changed between model versions" do
+        setup do
+          @wotsit = @widget.create_wotsit(name: "wotsit_0")
+          Timecop.travel 1.second.since
+          @new_widget = Widget.create(name: "new_widget")
+          @wotsit.update_attributes(widget_id: @new_widget.id, name: "wotsit_1")
+        end
+
+        context "when reified" do
+          setup { @wotsit_0 = @wotsit.versions.last.reify(belongs_to: true) }
+
+          should "see the association as it was at the time" do
+            assert_equal "widget_0", @wotsit_0.widget.name
+          end
+
+          should "not persist changes to the live association" do
+            assert_equal @new_widget, @wotsit.reload.widget
+          end
+        end
+
+        context "when reified with option mark_for_destruction" do
+          setup do
+            @wotsit_0 = @wotsit.versions.last.
+              reify(belongs_to: true, mark_for_destruction: true)
+          end
+
+          should "should not mark the new associated for destruction" do
+            assert_equal false, @new_widget.marked_for_destruction?
+          end
+        end
+      end
+    end
+  end
 end