Mongomapper and Sinatra undefined method `update_attributes' for nil:NilClass - ruby

Question

I getting the error "undefined method `update_attributes' for nil:NilClass" when using Sinatra with MongoMapper.
Model:
class Publication
include MongoMapper::Document
key :page, String
key :title, String
key :body, String
end
and code where i getting error:
post '/edit' do
#article = Publication.update({:page => 'main'}, {$set => {:title => params[:title], :body => params[:body]}})
end
i'm tried to make update in mongo console and it was successfully updated:
> db.publications.update({page: 'main'},{$set: {body: '333', title: '111'}})
> db.publications.find({page: 'main'})
{ "_id" : ObjectId("4fa45046530a6978e3000003"), "body" : "333", "page" : "main", "title" : "111" }
Full stack trace:
[2012-05-06 03:04:22] INFO WEBrick 1.3.1
[2012-05-06 03:04:22] INFO ruby 1.8.7 (2010-01-10) [universal-darwin11.0]
== Sinatra/1.3.2 has taken the stage on 4567 for development with backup from WEBrick
[2012-05-06 03:04:23] INFO WEBrick::HTTPServer#start: pid=32266 port=4567
localhost - - [06/May/2012:03:04:27 MSK] "GET /edit HTTP/1.1" 200 193
- -> /edit
localhost - - [06/May/2012:03:04:27 MSK] "GET /favicon.ico HTTP/1.1" 404 447
- -> /favicon.ico
NoMethodError - undefined method `update_attributes' for nil:NilClass:
/Library/Ruby/Gems/1.8/gems/mongo_mapper- 0.11.1/lib/mongo_mapper/plugins/querying.rb:118:in `update_single'
/Library/Ruby/Gems/1.8/gems/mongo_mapper-0.11.1/lib/mongo_mapper/plugins/querying.rb:117:in `tap'
/Library/Ruby/Gems/1.8/gems/mongo_mapper-0.11.1/lib/mongo_mapper/plugins/querying.rb:117:in `update_single'
/Library/Ruby/Gems/1.8/gems/mongo_mapper-0.11.1/lib/mongo_mapper/plugins/querying.rb:45:in `update'
main.rb:48:in `POST /edit'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:1211:in `call'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:1211:in `compile!'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:785:in `[]'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:785:in `route!'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:801:in `route_eval'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:785:in `route!'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:822:in `process_route'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:820:in `catch'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:820:in `process_route'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:784:in `route!'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:783:in `each'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:783:in `route!'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:886:in `dispatch!'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:719:in `call!'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:871:in `invoke'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:871:in `catch'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:871:in `invoke'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:719:in `call!'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:705:in `call'
/Library/Ruby/Gems/1.8/gems/rack-protection-1.2.0/lib/rack/protection/xss_header.rb:22:in `call'
/Library/Ruby/Gems/1.8/gems/rack-protection-1.2.0/lib/rack/protection/path_traversal.rb:16:in `call'
/Library/Ruby/Gems/1.8/gems/rack-protection-1.2.0/lib/rack/protection/json_csrf.rb:17:in `call'
/Library/Ruby/Gems/1.8/gems/rack-protection-1.2.0/lib/rack/protection/base.rb:47:in `call'
/Library/Ruby/Gems/1.8/gems/rack-protection-1.2.0/lib/rack/protection/xss_header.rb:22:in `call'
/Library/Ruby/Gems/1.8/gems/rack-1.4.1/lib/rack/logger.rb:15:in `call'
/Library/Ruby/Gems/1.8/gems/rack-1.4.1/lib/rack/head.rb:9:in `call'
/Library/Ruby/Gems/1.8/gems/rack-1.4.1/lib/rack/methodoverride.rb:21:in `call'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/showexceptions.rb:21:in `call'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:1334:in `call'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:1416:in `synchronize'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:1334:in `call'
/Library/Ruby/Gems/1.8/gems/rack-1.4.1/lib/rack/handler/webrick.rb:59:in `service'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/httpserver.rb:104:in `service'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/httpserver.rb:65:in `run'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/server.rb:173:in `start_thread'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/server.rb:162:in `start'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/server.rb:162:in `start_thread'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/server.rb:95:in `start'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/server.rb:92:in `each'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/server.rb:92:in `start'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/server.rb:23:in `start'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/webrick/server.rb:82:in `start'
/Library/Ruby/Gems/1.8/gems/rack-1.4.1/lib/rack/handler/webrick.rb:13:in `run'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/base.rb:1295:in `run!'
/Library/Ruby/Gems/1.8/gems/sinatra-1.3.2/lib/sinatra/main.rb:25
main.rb:53
anyone can say for what reason I do not get properly updated in the ruby code?

Answer 1

You probably meant to have :$set instead of $set as your key:
#article = Publication.update({:page => 'main'}, {:$set => {:title => params[:title], :body => params[:body]}})
What you have is using the global variable $set for the key, which is nil (since all global variables default to nil). For example:
{ $set => "something" } #=> {nil=>"something"}
{ :$set => "something" } #=> {:$set=>"something"}