Automatically restore has_one associations.

README.md

@@ -11,6 +11,7 @@ PaperTrail lets you track changes to your models' data.  It's good for auditing
 * Allows you to get at every version, including the original, even once destroyed.
 * Allows you to get at every version even if the schema has since changed.
 * Allows you to get at the version as of a particular time.
+* Automatically restores the `has_one` associations as they were at the time.
 * Automatically records who was responsible via your controller.  PaperTrail calls `current_user` by default, if it exists, but you can have it call any method you like.
 * Allows you to set who is responsible at model-level (useful for migrations).
 * Allows you to store arbitrary model-level metadata with each version (useful for filtering versions).
@@ -212,6 +213,27 @@ To find out who made a `version`'s object look that way, use `version.originator
     >> last_version.terminator                     # 'Bob'
 
 
+## Has-One Associations
+
+PaperTrail automatically restores `:has_one` associations as they were at the time.
+
+    class Treasure < ActiveRecord::Base
+      has_one :location
+    end
+
+    >> treasure.amount                  # 100
+    >> treasure.location.latitude       # 12.345
+
+    >> treasure.update_attributes :amount => 153
+    >> treasure.location.update_attributes :latitude => 54.321
+    
+    >> t = treasure.versions.last.reify
+    >> t.amount                         # 100
+    >> t.location.latitude              # 12.345
+    
+Unfortunately PaperTrail doesn't do this for `:has_many` associations (I can't get it to work) or `:belongs_to` (I ran out of time looking at `:has_many`).
+
+
 ## Has-Many-Through Associations
 
 PaperTrail can track most changes to the join table.  Specifically it can track all additions but it can only track removals which fire the `after_destroy` callback on the join table.  Here are some examples:

lib/paper_trail/has_paper_trail.rb

@@ -85,14 +85,10 @@ module PaperTrail
 
       # Returns the object (not a Version) as it was at the given timestamp.
       def version_at(timestamp)
-        # Short-circuit if the current state is applicable.
-        return self if self.updated_at <= timestamp
-        # Look for the first version created after, rather than before, the
-        # timestamp because a version stores how the object looked before the
-        # change.
-        version = versions.first :conditions => ['created_at > ?', timestamp],
-                                 :order      => 'created_at ASC'
-        version.try :reify
+        # Because a version stores how its object looked *before* the change,
+        # we need to look for the first version created *after* the timestamp.
+        version = versions.first :conditions => ['created_at > ?', timestamp], :order => 'created_at ASC, id ASC'
+        version ? version.reify : self
       end
 
       # Returns the object (not a Version) as it was most recently.
@@ -109,6 +105,17 @@ module PaperTrail
         subsequent_version.reify if subsequent_version
       end
 
+      protected
+
+      # Returns the object (not a Version) as it was until the version record
+      # with the given id.
+      def version_until(id)
+        # Because a version stores how its object looked *before* the change,
+        # we need to look for the first version created *on or after* the id.
+        version = versions.first :conditions => ['id >= ?', id], :order => 'id ASC'
+        version ? version.reify : self
+      end
+
       private
 
       def merge_metadata(data)

lib/paper_trail/version.rb

@@ -36,6 +36,10 @@ class Version < ActiveRecord::Base
       end
 
       model.version = self
+      # 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).
+      reify_has_ones model
       model
     end
   end
@@ -66,4 +70,21 @@ class Version < ActiveRecord::Base
                 :order => 'id ASC').index(self)
   end
 
+  private
+
+  def reify_has_ones(model)
+    model.class.reflect_on_all_associations(:has_one).each do |assoc|
+      child = model.send assoc.name
+      if child.respond_to? :version_until
+        if (version_until = child.version_until(id))
+          version_until.attributes.each do |k,v|
+            model.send(assoc.name).send "#{k}=", v rescue nil
+          end
+        else
+          model.send "#{assoc.name}=", nil
+        end
+      end
+    end
+  end
+
 end

test/paper_trail_model_test.rb

@@ -10,6 +10,7 @@ class FooWidget < Widget
 end
 
 class Wotsit < ActiveRecord::Base
+  has_paper_trail
   belongs_to :widget
 end
 
@@ -45,7 +46,8 @@ end
 
 class HasPaperTrailModelTest < Test::Unit::TestCase
   load_schema
-
+=begin
+=end
   context 'A record' do
     setup { @article = Article.create }
 
@@ -126,7 +128,8 @@ class HasPaperTrailModelTest < Test::Unit::TestCase
           end
 
           should 'copy the has_one association when reifying' do
-            assert_equal @wotsit, @reified_widget.wotsit
+            assert_nil @reified_widget.wotsit  # wotsit wasn't there at the last version
+            assert_equal @wotsit, @widget.wotsit  # wotsit came into being on the live object
           end
         end
 
@@ -644,4 +647,61 @@ class HasPaperTrailModelTest < Test::Unit::TestCase
     end
   end
 
+
+  context 'A model with a has_one association' do
+    setup { @widget = Widget.create :name => 'widget_0' }
+    context 'before the associated was created' do
+      setup do
+        @widget.update_attributes :name => 'widget_1'
+        @wotsit = @widget.create_wotsit :name => 'wotsit_0'
+      end
+      context 'when reified' do
+        setup { @widget_0 = @widget.versions.last.reify }
+        should 'see the associated as it was at the time' do
+          assert_nil @widget_0.wotsit
+        end
+      end
+    end
+
+    context 'where the associated is created between model versions' do
+      setup do
+        @wotsit = @widget.create_wotsit :name => 'wotsit_0'
+        @widget.update_attributes :name => 'widget_1'
+      end
+      context 'when reified' do
+        setup { @widget_0 = @widget.versions.last.reify }
+        should 'see the associated as it was at the time' do
+          assert_equal 'wotsit_0', @widget_0.wotsit.name
+        end
+      end
+
+      context 'and then the associated is updated between model versions' do
+        setup do
+          @wotsit.update_attributes :name => 'wotsit_1'
+          @wotsit.update_attributes :name => 'wotsit_2'
+          @widget.update_attributes :name => 'widget_2'
+        end
+        context 'when reified' do
+          setup { @widget_1 = @widget.versions.last.reify }
+          should 'see the associated as it was at the time' do
+            assert_equal 'wotsit_2', @widget_1.wotsit.name
+          end
+        end
+      end
+
+      context 'and then the associated is destroyed between model versions' do
+        setup do
+          @wotsit.destroy
+          @widget.update_attributes :name => 'widget_3'
+        end
+        context 'when reified' do
+          setup { @widget_2 = @widget.versions.last.reify }
+          should 'see the associated as it was at the time' do
+            assert_nil @widget_2.wotsit
+          end
+        end
+      end
+    end
+  end
+
 end

test/schema.rb

@@ -37,6 +37,7 @@ ActiveRecord::Schema.define(:version => 0) do
   create_table :wotsits, :force => true do |t|
     t.integer :widget_id
     t.string  :name
+    t.datetime :created_at, :updated_at
   end
 
   create_table :fluxors, :force => true do |t|