the :default_url option for has_attached_file can now also be a Proc/lamba,…

the :default_url option for has_attached_file can now also be a Proc/lamba, which gets executed *before* it gets interpolated

Closes #253, Closes #360

lib/paperclip/attachment.rb

@@ -123,7 +123,8 @@ module Paperclip
     # security, however, for performance reasons. Set use_timestamp to false
     # if you want to stop the attachment update time appended to the url
     def url(style_name = default_style, use_timestamp = @use_timestamp)
-      url = original_filename.nil? ? interpolate(@default_url, style_name) : interpolate(@url, style_name)
+      default_url = @default_url.is_a?(Proc) ? @default_url.call(self) : @default_url
+      url = original_filename.nil? ? interpolate(default_url, style_name) : interpolate(@url, style_name)
       use_timestamp && updated_at ? [url, updated_at].compact.join(url.include?("?") ? "&" : "?") : url
     end
 

test/attachment_test.rb

@@ -14,6 +14,28 @@ class AttachmentTest < Test::Unit::TestCase
     assert_equal "#{Rails.root}/public/fake_models/1234/fake", @attachment.path
   end
 
+  should "return the url by interpolating the default_url option when no file assigned" do
+    @attachment = attachment :default_url => ":class/blegga.png"
+    @model = @attachment.instance
+    assert_nil @model.avatar_file_name
+    assert_equal "fake_models/blegga.png", @attachment.url
+  end
+
+  should "return the url by executing and interpolating the default_url Proc when no file assigned" do
+    @attachment = attachment :default_url => lambda { |a| ":class/blegga.png" }
+    @model = @attachment.instance
+    assert_nil @model.avatar_file_name
+    assert_equal "fake_models/blegga.png", @attachment.url
+  end
+
+  should "return the url by executing and interpolating the default_url Proc with attachment arg when no file assigned" do
+    @attachment = attachment :default_url => lambda { |a| a.instance.some_method_to_determine_default_url }
+    @model = @attachment.instance
+    @model.stubs(:some_method_to_determine_default_url).returns(":class/blegga.png")
+    assert_nil @model.avatar_file_name
+    assert_equal "fake_models/blegga.png", @attachment.url
+  end
+
   context "Attachment default_options" do
     setup do
       rebuild_model