Cache instance_read/_write. Make content_type validation work even with no _content_type field

lib/paperclip.rb

@@ -258,6 +258,9 @@ module Paperclip
     #   match.  Allows all by default.
     # * +message+: The message to display when the uploaded file has an invalid
     #   content type.
+    # NOTE: If you do not specify an [attachment]_content_type field on your
+    # model, content_type validation will work _ONLY upon assignment_ and
+    # re-validation after the instance has been reloaded will always succeed.
     def validates_attachment_content_type name, options = {}
       attachment_definitions[name][:validations][:content_type] = lambda do |attachment, instance|
         valid_types = [options[:content_type]].flatten
@@ -265,7 +268,7 @@ module Paperclip
         unless attachment.original_filename.blank?
           unless valid_types.blank?
             content_type = attachment.instance_read(:content_type)
-            unless valid_types.any?{|t| t === content_type }
+            unless valid_types.any?{|t| content_type.nil? || t === content_type }
               options[:message] || "is not one of the allowed file types."
             end
           end

lib/paperclip/attachment.rb

@@ -243,6 +243,7 @@ module Paperclip
     def instance_write(attr, value)
       setter = :"#{name}_#{attr}="
       responds = instance.respond_to?(setter)
+      self.instance_variable_set("@_#{setter.to_s.chop}", value)
       instance.send(setter, value) if responds || attr.to_s == "file_name"
     end
 
@@ -251,6 +252,8 @@ module Paperclip
     def instance_read(attr)
       getter = :"#{name}_#{attr}"
       responds = instance.respond_to?(getter)
+      cached = self.instance_variable_get("@_#{getter}")
+      return cached if cached
       instance.send(getter) if responds || attr.to_s == "file_name"
     end
 

test/attachment_test.rb

@@ -582,8 +582,16 @@ class AttachmentTest < Test::Unit::TestCase
       assert_nothing_raised { @dummy.avatar = @file }
     end
 
-    should "return nil when sent #avatar_updated_at" do
+    should "return the time when sent #avatar_updated_at" do
+      now = Time.now
+      Time.stubs(:now).returns(now)
       @dummy.avatar = @file
+      assert now, @dummy.avatar.updated_at
+    end
+
+    should "return nil when reloaded and sent #avatar_updated_at" do
+      @dummy.save
+      @dummy.reload
       assert_nil @dummy.avatar.updated_at
     end