nested structures with build_query_string

hi all!

just recently i encountered a problem when giving a hash to
ActionController::Base#url_for that itself includes a hash, e.g.,
{:action => 'search', :query => {:field1 => 'value1', :field2 =>
'value2'}}.

the corresponding URL looks like
"/search?query[field1]=value1&query[field2]=value2&commit=Search".

however, the URL built by url_for looks like this:
"/search?query=field1value1field2value2&commit=Search" -- which is
obviously incorrect.

this is caused by ActionController::UrlRewriter#build_query_string,
which does recognize arrays, but not hashes. rewriting that method
to build the query string recursively for nested structures lead to
the following:

---- snip ----
def build_query_string(hash, only_keys = nil)
  elements = []

  build_element = lambda { |key, value|
    # skip empty params
    return if value.nil? or value.empty?

    case value
      when Array
        value.each { |v|
          build_element.call "#{key}[]", v
        }
      when Hash
        value.each_pair { |k, v|
          build_element.call "#{key}[#{k}]", v
         }
      else
        elements << "#{key}=#{Routing.extract_parameter_value(value)}"
    end
  }

  (only_keys || hash.keys).each { |key|
    build_element.call CGI.escape(key.to_s), hash[key]
  }

  elements.empty? ? '' : '?' + elements.join('&')
end
---- snip ----

this works for the above mentioned case, nonetheless a few questions
arise:

1. what do you think about this? does it make sense? is it "good" ruby?

2. where shall i put the modified method? in my lib/ directory i
have util/extensions/* which all get included in environment.rb --
this, however, didn't seem to work. webrick spits out warnings

./script/../config/../vendor/rails/actionpack/lib/action_controller/routing.rb:660:
warning: already initialized constant Helpers
./script/../config/../vendor/rails/actionpack/lib/action_controller/routing.rb:714:
warning: already initialized constant Routes

and i get the following exception: "No url can be generated for the
hash [...]". modifying action_controller/url_rewriter.rb in place
wouldn't be the preferred way to go, now would it...

thanks for your comments.

cheers
jens