short-circuit the logic in extract_attribute to fix performance regre…

…ssion

lib/mongoid/matcher.rb

@@ -44,6 +44,13 @@ module Matcher
     #
     # @return [ Object | Array ] Field value or values.
     module_function def extract_attribute(document, key)
+      # Performance optimization; if the key does not include a '.' character,
+      # it must reference an immediate attribute of the document.
+      unless key.include?('.')
+        hash = document.respond_to?(:attributes) ? document.attributes : document
+        return [ hash[key] ] if hash.key?(key)
+      end
+
       if document.respond_to?(:as_attributes, true)
         # If a document has hash fields, as_attributes would keep those fields
         # as Hash instances which do not offer indifferent access.

spec/mongoid/association/referenced/belongs_to/proxy_spec.rb

@@ -751,6 +751,10 @@
           person.save!
         end
 
+        # NOTE: there as a bad interdependency here, with the auto_save_spec.rb
+        # file. If auto_save_spec.rb runs before this, the following specs fail
+        # with "undefined method `nullify' for an instance of Person".
+
         context "when parent exists" do
 
           context "when child is destroyed" do