Mongomapper和Sinatra未定義方法`update_attributes'爲零：NilClass

Question

當使用Sinatra和MongoMapper時，出現錯誤「未定義方法`update_attributes'爲零：NilClass」。

型號：

class Publication 
include MongoMapper::Document 

key :page, String 
key :title, String 
key :body, String 
end 

和代碼在那裏我得到錯誤：

post '/edit' do 
@article = Publication.update({:page => 'main'}, {$set => {:title => params[:title], :body => params[:body]}}) 
end 

我正在試圖使更新的蒙戈控制檯，它已成功更新：

> db.publications.update({page: 'main'},{$set: {body: '333', title: '111'}}) 
> db.publications.find({page: 'main'}) 
{ "_id" : ObjectId("4fa45046530a6978e3000003"), "body" : "333", "page" : "main", "title" : "111" } 

完全堆棧跟蹤：

[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 

任何人都可以說，什麼原因，我沒有得到正確的Ruby代碼更新？

Answer 1

你可能意味着有:$set而不是$set爲你的關鍵：

@article = Publication.update({:page => 'main'}, {:$set => {:title => params[:title], :body => params[:body]}}) 

你必須使用全局變量$set爲重點，這是nil（因爲所有的全局變量默認爲nil）什麼。例如：

{ $set => "something" } #=> {nil=>"something"} 
{ :$set => "something" } #=> {:$set=>"something"}