Fixed ID partitioning interpolation, when cloning attachments

lib/paperclip/interpolations.rb

@@ -150,10 +150,13 @@ module Paperclip
     # Returns the id of the instance in a split path form. e.g. returns
     # 000/001/234 for an id of 1234.
     def id_partition attachment, style_name
-      if (id = attachment.instance.id).is_a?(Integer)
+      case id = attachment.instance.id
+      when Integer
         ("%09d" % id).scan(/\d{3}/).join("/")
-      else
+      when String
         id.scan(/.{3}/).first(3).join("/")
+      else
+        nil
       end
     end
 

test/interpolations_test.rb

@@ -88,6 +88,13 @@ class InterpolationsTest < Test::Unit::TestCase
     assert_equal 23, Paperclip::Interpolations.id(attachment, :style)
   end
 
+  should "return nil for attachments to new records" do
+    attachment = mock
+    attachment.expects(:id).returns(nil)
+    attachment.expects(:instance).returns(attachment)
+    assert_nil Paperclip::Interpolations.id(attachment, :style)
+  end
+
   should "return the partitioned id of the attachment when the id is an integer" do
     attachment = mock
     attachment.expects(:id).returns(23)
@@ -102,6 +109,13 @@ class InterpolationsTest < Test::Unit::TestCase
     assert_equal "32f/nj2/3oi", Paperclip::Interpolations.id_partition(attachment, :style)
   end
 
+  should "return nil for the partitioned id of an attachment to a new record (when the id is nil)" do
+    attachment = mock
+    attachment.expects(:id).returns(nil)
+    attachment.expects(:instance).returns(attachment)
+    assert_nil Paperclip::Interpolations.id_partition(attachment, :style)
+  end
+
   should "return the name of the attachment" do
     attachment = mock
     attachment.expects(:name).returns("file")