validation for tags

models/comment_thread.rb

@@ -32,6 +32,8 @@ class CommentThread < Content
   validates_presence_of :course_id # do we really need this?
   validates_presence_of :commentable_id
 
+  validate :valid_tag_names
+
   after_create :generate_notifications
 
   def root_comments
@@ -94,5 +96,11 @@ private
     end
   end
 
+  def valid_tag_names
+    unless tags_array.all? {|tag| tag =~ /^\w+(\s*\w+)*$/}
+      errors.add :tag, "must consist of words, numbers, underscores and spaces only"
+    end
+  end
+
   handle_asynchronously :generate_notifications
 end