fixes #357

app/models/post_version.rb

@@ -105,6 +105,30 @@ class PostVersion < ActiveRecord::Base
     }
   end
 
+  def changes
+    @changes ||= diff(previous)
+  end
+
+  def added_tags
+    changes[:added_tags].join(" ")
+  end
+
+  def removed_tags
+    changes[:removed_tags].join(" ")
+  end
+
+  def obsolete_added_tags
+    changes[:obsolete_added_tags].join(" ")
+  end
+
+  def obsolete_removed_tags
+    changes[:obsolete_removed_tags].join(" ")
+  end
+
+  def unchanged_tags
+    changes[:unchanged_tags].join(" ")
+  end
+
   def previous
     PostVersion.where("post_id = ? and updated_at < ?", post_id, updated_at).order("updated_at desc").first
   end
@@ -141,4 +165,23 @@ class PostVersion < ActiveRecord::Base
     undo
     post.save!
   end
+
+  def serializable_hash(options = {})
+    options ||= {}
+    options[:except] ||= []
+    options[:except] += hidden_attributes
+    unless options[:builder]
+      options[:methods] ||= []
+      options[:methods] += [:added_tags, :removed_tags, :obsolete_added_tags, :obsolete_removed_tags, :unchanged_tags]
+    end
+    hash = super(options)
+    hash
+  end
+
+  def to_xml(options = {}, &block)
+    options ||= {}
+    options[:methods] ||= []
+    options[:methods] += [:added_tags, :removed_tags, :obsolete_added_tags, :obsolete_removed_tags, :unchanged_tags]
+    super(options, &block)
+  end
 end