1 files changed, 10 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 4a637d5dab..2861a3940b 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -66,6 +66,16 @@ module ActiveRecord
     end
   end
 
+  class ReadOnlyAssociation < ActiveRecordError #:nodoc:
+    def initialize(reflection)
+      @reflection = reflection
+    end
+  
+    def message
+      "Can not add to a has_many :through association.  Try adding to #{@reflection.through_reflection.name.inspect}."
+    end
+  end
+
   module Associations # :nodoc:
     def self.append_features(base)
       super