has_attached_file will raise if the _file_size and _content_type fields don't exist.

lib/paperclip.rb

@@ -113,6 +113,12 @@ module Paperclip
     def has_attached_file name, options = {}
       include InstanceMethods
 
+      %w(file_name content_type).each do |field|
+        unless column_names.include?("#{name}_#{field}")
+          raise PaperclipError.new("#{self} model does not have required column '#{name}_#{field}'")
+        end
+      end
+
       write_inheritable_attribute(:attachment_definitions, {}) if attachment_definitions.nil?
       attachment_definitions[name] = {:validations => []}.merge(options)
 

test/paperclip_test.rb

@@ -7,6 +7,14 @@ class PaperclipTest < Test::Unit::TestCase
       @file = File.new(File.join(FIXTURES_DIR, "5k.png"))
     end
 
+    should "error when trying to also create a 'blah' attachment" do
+      assert_raises(Paperclip::PaperclipError) do
+        Dummy.class_eval do
+          has_attached_file :blah
+        end
+      end
+    end
+
     context "that is attr_protected" do
       setup do
         Dummy.class_eval do