Allow assigning another paperclip: new_user.avatar = old_user.avatar.

lib/paperclip/attachment.rb

@@ -50,7 +50,13 @@ def initialize name, instance, options = {}
     # What gets called when you call instance.attachment = File. It clears errors,
     # assigns attributes, processes the file, and runs validations. It also queues up
     # the previous file for deletion, to be flushed away on #save of its host.
+    # In addition to form uploads, you can also assign another Paperclip attachment:
+    #   new_user.avatar = old_user.avatar
     def assign uploaded_file
+      if uploaded_file.is_a?(Paperclip::Attachment)
+        uploaded_file = uploaded_file.to_file(:original)
+      end
+
       return nil unless valid_assignment?(uploaded_file)
       logger.info("[paperclip] Assigning #{uploaded_file} to #{name}")
 

test/integration_test.rb

@@ -198,6 +198,21 @@ class IntegrationTest < Test::Unit::TestCase
       @dummy.reload
       assert_equal "5k.png", @dummy.avatar_file_name
     end
+
+    should "assign images from other Paperclips as well" do
+      @dummy2 = Dummy.new
+      @file2  = File.new(File.join(FIXTURES_DIR, "12k.png"))
+      assert  @dummy2.avatar = @file2
+      @dummy2.save
+
+      assert_not_equal `identify -format "%wx%h" #{@dummy.avatar.to_file(:original).path}`,
+                       `identify -format "%wx%h" #{@dummy2.avatar.to_file(:original).path}`
+
+      assert @dummy.avatar = @dummy2.avatar
+      @dummy.save
+      assert_equal `identify -format "%wx%h" #{@dummy.avatar.to_file(:original).path}`,
+                   `identify -format "%wx%h" #{@dummy2.avatar.to_file(:original).path}`
+    end
   end
 
   if ENV['S3_TEST_BUCKET']