diff --git a/README.rdoc b/README.rdoc
index 1195065..eee3679 100644
--- a/README.rdoc
+++ b/README.rdoc
@@ -2,8 +2,8 @@
 
 Rack:GridFS is a Rack middleware for creating HTTP endpoints for files
 stored in MongoDB's GridFS.  You can configure a prefix string which
-will be used to match the path of a request and supply an id for looking
-up the file in the GridFS store.
+will be used to match the path of a request, and further look up GridFS
+files based on either their +ObjectId+ or +filename+ field.
 
 For example,
 
@@ -24,28 +24,101 @@ to the GridFS API prior to v1.0, you may have luck with the git-tagged version
 == Usage
 
   require 'rack/gridfs'
-  use Rack::GridFS, :hostname => 'localhost', :port => 27017, :database => 'test', :prefix => 'gridfs'
+  use Rack::GridFS, :prefix => 'gridfs', :hostname => 'localhost', :port => 27017, :database => 'test'
 
-You must specify MongoDB database details:
-- hostname: the hostname/IP where the MongoDB server is running.  Default 'localhost'.
-- port: the port of the MongoDB server.  Default 27017.
-- database: the MongoDB database to connect to.
-- prefix: a string used to match against incoming paths and route to through the middleware.  Default 'gridfs'.
+Options:
+- +prefix+: a string used to match against incoming paths and route to through
+  the middleware.  Default 'gridfs'.
+- +lookup+: whether to look up a file based on <tt>:id</tt> or <tt>:path</tt>
+  (example below).  Default is <tt>:id</tt>.
 
-== Sinatra Example
+You must also specify MongoDB database details:
+- +hostname+: the hostname/IP where the MongoDB server is running.  Default 'localhost'.
+- +port+: the port of the MongoDB server.  Default 27017.
+- +database+: the name of the MongoDB database to connect to.
+- +username+ and +password+: if you need to authenticate to MongoDB.
 
-  # TODO: THIS COULD USE A LOT MORE EXPLANATION!
+=== Simple Sinatra Example
 
   require 'rubygems'
   require 'sinatra'
 
   require 'rack/gridfs'
-  use Rack::GridFS, :hostname => 'localhost', :port => 27017, :database => 'test', :prefix => 'gridfs'
+  use Rack::GridFS, :database => 'test', :prefix => 'gridfs'
 
   get /.*/ do
     "The URL did not match a file in GridFS."
   end
 
+=== Usage with Rails
+
+To use <tt>Rack::GridFS</tt> in a Rails application, add it as middleware in
+<tt>application.rb</tt> or <tt>config/environments/*</tt>with something like this:
+
+  config.middleware.insert_after Rack::Runtime, Rack::GridFS,
+    :prefix => 'uploads', :database => "my_app_#{Rails.env}"
+
+Run <tt>rake middleware</tt> to decide for yourself where to best place it in
+the middleware stack for your app using {the Rails convenience methods}[http://guides.rubyonrails.org/rails_on_rack.html#configuring-middleware-stack],
+taking into consideration that it can probably be near the top since it simply
+returns a "static" file or a 404.
+
+=== Path (filename) Lookup
+
+The <tt>:lookup => :path</tt> option causes files to be looked up from the GridFS
+store based on their +filename+ field (which can be a full file path) rather than
++ObjectId+ (requests still need to match the +prefix+ you've set). This allows
+you to find files based on essentially arbitrary URLs such as:
+
+    GET '/prefix/media/images/jane_avatar.jpg'
+
+How filenames are set is specific to your application. We'll look at an example
+with Carrierwave below.
+
+*NOTE*: The Mongo Ruby driver will try to create an index on the +filename+
+field for you automatically, but if you are using filename lookup you'll want to
+double-check that it is created appropriately (on slaves only if you have a
+master-slave architecture, etc.).
+
+=== Carrierwave Example
+
+Path lookup works well for usage with Carrierwave[https://github.com/jnicklas/carrierwave].
+As a minimal example with Mongoid:
+
+  # config/initializers/carrierwave.rb
+  CarrierWave.configure do |config|
+    config.storage = :grid_fs
+    config.grid_fs_connection = Mongoid.database
+    config.grid_fs_access_url = "/uploads"
+  end
+
+  # app/uploaders/avatar_uploader.rb
+  class AvatarUploader < CarrierWave::Uploader::Base
+    # (Virtual) path where uploaded files will be stored, appended to the
+    # gridfs_access_url by methods used with view helpers
+    def store_dir
+      "#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
+    end
+  end
+
+  # app/models/user.rb
+  class User
+    include Mongoid::Document
+    mount_uploader :avatar, AvatarUploader
+  end
+
+  # app/views/user/show.html.erb
+  <%= image_tag(@user.avatar.url) if @user.avatar? %>
+
+This will result in URL paths like <tt>/uploads/user/avatar/4d250d04a8f41c0a31000006/original_filename.jpg</tt>
+being generated for the view helpers, and Carrierwave will store
+<tt>user/avatar/4d250d04a8f41c0a31000006/original_filename.jpg</tt> as the
++filename+ in GridFS. Thus, you can configure <tt>Rack::GridFS</tt> to serve
+these files as such:
+
+  config.middleware.insert_after Rack::Runtime, Rack::GridFS,
+    :prefix => 'uploads', :lookup => :path, :database => "my_app_#{Rails.env}"
+
 == Copyright
 
 Copyright (c) 2010 Blake Carlson. See LICENSE for details.
diff --git a/lib/rack/gridfs.rb b/lib/rack/gridfs.rb
index 17a5a76..79535d6 100644
--- a/lib/rack/gridfs.rb
+++ b/lib/rack/gridfs.rb
@@ -2,25 +2,22 @@
 require 'mongo'
 
 module Rack
-
   class GridFSConnectionError < StandardError ; end
 
   class GridFS
     VERSION = "0.2.0"
 
-    attr_reader :hostname, :port, :database, :prefix, :db
-
     def initialize(app, options = {})
       options = {
         :hostname => 'localhost',
-        :prefix   => 'gridfs',
         :port     => Mongo::Connection::DEFAULT_PORT,
-        :accessor => 'id'
+        :prefix   => 'gridfs',
+        :lookup   => :id
       }.merge(options)
 
       @app        = app
       @prefix     = options[:prefix]
-      @accessor   = options[:accessor]
+      @lookup     = options[:lookup]
       @db         = nil
 
       @hostname, @port, @database, @username, @password = 
@@ -31,34 +28,36 @@ def initialize(app, options = {})
 
     def call(env)
       request = Rack::Request.new(env)
-      if request.path_info =~ /^\/#{prefix}\/(.+)$/
+      if request.path_info =~ /^\/#{@prefix}\/(.+)$/
         gridfs_request($1)
       else
         @app.call(env)
       end
     end
 
-    def gridfs_request(path)
-      if @accessor == 'id'
-        file = Mongo::Grid.new(db).get(BSON::ObjectId.from_string(path))
-      elsif @accessor == 'path'
-        file = Mongo::GridFileSystem.new(db).open(path, "r")
-      end
-      [200, {'Content-Type' => file.content_type}, file]
-    rescue Mongo::GridFileNotFound, BSON::InvalidObjectId
-      [404, {'Content-Type' => 'text/plain'}, ['File not found.']]
-    end
-
     private
       def connect!
         Timeout::timeout(5) do
-          @db = Mongo::Connection.new(hostname, port).db(database)
+          @db = Mongo::Connection.new(@hostname, @port).db(@database)
           @db.authenticate(@username, @password) if @username
         end
       rescue Exception => e
         raise Rack::GridFSConnectionError, "Unable to connect to the MongoDB server (#{e.to_s})"
       end
 
-  end
+      def gridfs_request(identifier)
+        file = find_file(identifier)
+        [200, {'Content-Type' => file.content_type}, file]
+      rescue Mongo::GridFileNotFound, BSON::InvalidObjectId
+        [404, {'Content-Type' => 'text/plain'}, ['File not found.']]
+      end
+
+      def find_file(identifier)
+        case @lookup.to_sym
+        when :id   then Mongo::Grid.new(@db).get(BSON::ObjectId.from_string(identifier))
+        when :path then Mongo::GridFileSystem.new(@db).open(identifier, "r")
+        end
+      end
 
-end
+  end # GridFS class
+end # Rack module
diff --git a/test/gridfs_test.rb b/test/gridfs_test.rb
index 952dcf7..8f55f53 100644
--- a/test/gridfs_test.rb
+++ b/test/gridfs_test.rb
@@ -15,66 +15,103 @@ def db
     @db ||= Mongo::Connection.new(test_database_options[:hostname], test_database_options[:port]).db(test_database_options[:database])
   end
 
-  def app
-    gridfs_opts = test_database_options
+  def setup_app(opts={})
+    gridfs_opts = test_database_options.merge(opts)
     Rack::Builder.new do
       use Rack::GridFS, gridfs_opts
       run lambda { |env| [200, {'Content-Type' => 'text/plain'}, ["Hello, World!"]] }
     end
   end
 
-  def load_artifact(filename, content_type)
+  def load_artifact(filename, content_type, path=nil)
     contents = File.read(File.join(File.dirname(__FILE__), 'artifacts', filename))
-    Mongo::Grid.new(db).put(contents, :filename => filename, :content_type => content_type)
+    if path
+      grid = Mongo::GridFileSystem.new(db)
+      file = [path, filename].join('/')
+      grid.open(file, 'w') { |f| f.write contents }
+      grid.open(file, 'r')
+    else      
+      Mongo::Grid.new(db).put(contents, :filename => filename, :content_type => content_type)
+    end
   end
 
   context "Rack::GridFS" do
+    setup do
+      def app; setup_app end
+    end
 
     context "on initialization" do
 
       setup do
         stub_mongodb_connection
-        @options = { :hostname => 'myhostname.mydomain', :port => 8765, :database => 'mydatabase', :prefix => 'myprefix' }
+        @options = {
+          :hostname => 'myhostname.mydomain',
+          :port => 8765,
+          :database => 'mydatabase',
+          :prefix => 'myprefix',
+          :username => 'bob',
+          :password => 'so-s3cur3'
+        }
       end
 
       should "have a hostname option" do
         mware = Rack::GridFS.new(nil, @options)
-        assert_equal @options[:hostname], mware.hostname
+        assert_equal @options[:hostname], mware.instance_variable_get(:@hostname)
       end
 
       should "have a default hostname" do
         mware = Rack::GridFS.new(nil, @options.except(:hostname))
-        assert_equal 'localhost', mware.hostname
+        assert_equal 'localhost', mware.instance_variable_get(:@hostname)
       end
 
       should "have a port option" do
         mware = Rack::GridFS.new(nil, @options)
-        assert_equal @options[:port], mware.port
+        assert_equal @options[:port], mware.instance_variable_get(:@port)
       end
 
       should "have a default port" do
         mware = Rack::GridFS.new(nil, @options.except(:port))
-        assert_equal Mongo::Connection::DEFAULT_PORT, mware.port
+        assert_equal Mongo::Connection::DEFAULT_PORT, mware.instance_variable_get(:@port)
       end
 
       should "have a database option" do
         mware = Rack::GridFS.new(nil, @options)
-        assert_equal @options[:database], mware.database
+        assert_equal @options[:database], mware.instance_variable_get(:@database)
       end
 
       should "not have a default database" do
         mware = Rack::GridFS.new(nil, @options.except(:database))
-        assert_nil mware.database
+        assert_nil mware.instance_variable_get(:@database)
       end
 
       should "have a prefix option" do
         mware = Rack::GridFS.new(nil, @options)
-        assert_equal mware.prefix, @options[:prefix]
+        assert_equal mware.instance_variable_get(:@prefix), @options[:prefix]
       end
 
       should "have a default prefix" do
         mware = Rack::GridFS.new(nil, @options.except(:prefix))
-        assert_equal mware.prefix, 'gridfs'
+        assert_equal mware.instance_variable_get(:@prefix), 'gridfs'
+      end
+
+      should "have a username option" do
+        mware = Rack::GridFS.new(nil, @options)
+        assert_equal @options[:username], mware.instance_variable_get(:@username)
+      end
+
+      should "have a password option" do
+        mware = Rack::GridFS.new(nil, @options)
+        assert_equal @options[:password], mware.instance_variable_get(:@password)
+      end
+
+      should "not have a default username" do
+        mware = Rack::GridFS.new(nil, @options.except(:username))
+        assert_nil mware.instance_variable_get(:@username)
+      end
+
+      should "not have a default password" do
+        mware = Rack::GridFS.new(nil, @options.except(:password))
+        assert_nil mware.instance_variable_get(:@password)
       end
 
       should "connect to the MongoDB server" do
@@ -92,7 +129,7 @@ def load_artifact(filename, content_type)
       end
     end
 
-    context "with files in GridFS" do
+    context "for lookup by ObjectId" do
       setup do
         @text_id = load_artifact('test.txt', 'text/plain')
         @html_id = load_artifact('test.html', 'text/html')
@@ -135,6 +172,50 @@ def load_artifact(filename, content_type)
       end
     end
 
+    context "for lookup by filename" do
+      setup do
+        def app; setup_app(:lookup => :path) end
+        @text_file = load_artifact('test.txt', nil, path='text')
+        @html_file = load_artifact('test.html', nil, path='html')
+      end
+
+      teardown do
+        db.collection('fs.files').remove
+      end
+
+      should "return TXT files stored in GridFS" do
+        get "/gridfs/#{@text_file.filename}"
+        assert_equal "Lorem ipsum dolor sit amet.", last_response.body
+      end
+
+      should "return the proper content type for TXT files" do
+        get "/gridfs/#{@text_file.filename}"
+        assert_equal 'text/plain', last_response.content_type
+      end
+
+      should "return HTML files stored in GridFS" do
+        get "/gridfs/#{@html_file.filename}"
+        assert_match /html.*?body.*Test/m, last_response.body
+      end
+
+      should "return the proper content type for HTML files" do
+        get "/gridfs/#{@html_file.filename}"
+        assert_equal 'text/html', last_response.content_type
+      end
+
+      should "return a not found for a unknown path" do
+        get '/gridfs/unknown'
+        assert last_response.not_found?
+      end
+
+      should "work for small images" do
+        image_id = load_artifact('3wolfmoon.jpg', nil, 'images')
+        get "/gridfs/#{image_id.filename}"
+        assert last_response.ok?
+        assert_equal 'image/jpeg', last_response.content_type
+      end
+    end
+
   end
 
 end