我遇到了 form_for 的问题，已经搜索了问题，给出的解决方案并不能解决我的问题。
我正在尝试制作一个表格来创建新食谱：
**app/views/recipes/new.html.erb**
<%= form_for @recipe do |f| %>
<% if @recipe.errors.any? %>
<% end %>
<div class="field">
<%= f.label :recipename %><br />
<%= f.text_area :recipename %>
</div>
<div class="field">
<%= f.label :user_id %><br />
<%= f.number_field :user_id %>
</div>
<div class="actions">
<%= f.submit %>
</div>
**routes.rb**
Baserecipe::Application.routes.draw do
resources :users
resources :recipes
....
match '/createrecipe', to: 'recipes#new'
**recipes_controller.rb**
class RecipesController < ApplicationController
def create
@recipe = Recipe.new(params[:recipe])
end
end
我总是收到错误：
undefined method `model_name' for NilClass:Class
提取的源代码（在第 1 行附近）：
1: <%= form_for @recipe do |f| %>
2: <% if @recipe.errors.any? %>
3: <% end %>
class Recipe < ActiveRecord::Base
attr_accessible :recipename, :instruct1, :instruct2, :instruct3, :instruct4, :instruct5,
:instruct6, :instruct7, :instruct8, :instruct9, :instruct10, :instruct11, :instruct12,
:instruct13, :instruct14, :instruct15, :instruct16, :instruct17, :instruct18, :instruct19,
:instruct20, :instruct21, :instruct22, :instruct23, :instruct24, :instruct25, :instruct26,
:instruct27, :instruct28, :instruct29, :instruct30, :preptime, :cooktime
belongs_to :user
has_many :ingredients
has_many :rcomments
validates :recipename, presence: true, length: { maximum: 140 }
validates :user_id, presence: true
validates :preptime, presence: true
validates :cooktime, presence: true
default_scope order: 'recipes.created_at DESC'
end
完整的跟踪：
activemodel (3.2.7) lib/active_model/naming.rb:163:in `model_name_from_record_or_class'
activemodel (3.2.7) lib/active_model/naming.rb:158:in `param_key'
actionpack (3.2.7) lib/action_view/helpers/form_helper.rb:369:in `form_for'
app/views/recipes/new.html.erb:3:in `_app_views_recipes_new_html_erb___168565054_39061080'
actionpack (3.2.7) lib/action_view/template.rb:145:in `block in render'
activesupport (3.2.7) lib/active_support/notifications.rb:125:in `instrument'
actionpack (3.2.7) lib/action_view/template.rb:143:in `render'
actionpack (3.2.7) lib/action_view/renderer/template_renderer.rb:47:in `block (2 levels) in render_template'
actionpack (3.2.7) lib/action_view/renderer/abstract_renderer.rb:38:in `block in instrument'
activesupport (3.2.7) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.7) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.7) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.7) lib/action_view/renderer/abstract_renderer.rb:38:in `instrument'
actionpack (3.2.7) lib/action_view/renderer/template_renderer.rb:46:in `block in render_template'
actionpack (3.2.7) lib/action_view/renderer/template_renderer.rb:54:in `render_with_layout'
actionpack (3.2.7) lib/action_view/renderer/template_renderer.rb:45:in `render_template'
actionpack (3.2.7) lib/action_view/renderer/template_renderer.rb:18:in `render'
actionpack (3.2.7) lib/action_view/renderer/renderer.rb:36:in `render_template'
actionpack (3.2.7) lib/action_view/renderer/renderer.rb:17:in `render'
actionpack (3.2.7) lib/abstract_controller/rendering.rb:110:in `_render_template'
actionpack (3.2.7) lib/action_controller/metal/streaming.rb:225:in `_render_template'
actionpack (3.2.7) lib/abstract_controller/rendering.rb:103:in `render_to_body'
actionpack (3.2.7) lib/action_controller/metal/renderers.rb:28:in `render_to_body'
actionpack (3.2.7) lib/action_controller/metal/compatibility.rb:50:in `render_to_body'
actionpack (3.2.7) lib/abstract_controller/rendering.rb:88:in `render'
actionpack (3.2.7) lib/action_controller/metal/rendering.rb:16:in `render'
actionpack (3.2.7) lib/action_controller/metal/instrumentation.rb:40:in `block (2 levels) in render'
activesupport (3.2.7) lib/active_support/core_ext/benchmark.rb:5:in `block in ms'
c:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/benchmark.rb:295:in `realtime'
activesupport (3.2.7) lib/active_support/core_ext/benchmark.rb:5:in `ms'
actionpack (3.2.7) lib/action_controller/metal/instrumentation.rb:40:in `block in render'
actionpack (3.2.7) lib/action_controller/metal/instrumentation.rb:83:in `cleanup_view_runtime'
activerecord (3.2.7) lib/active_record/railties/controller_runtime.rb:24:in `cleanup_view_runtime'
actionpack (3.2.7) lib/action_controller/metal/instrumentation.rb:39:in `render'
actionpack (3.2.7) lib/action_controller/metal/implicit_render.rb:10:in `default_render'
actionpack (3.2.7) lib/action_controller/metal/implicit_render.rb:5:in `send_action'
actionpack (3.2.7) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.2.7) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.2.7) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.2.7) lib/active_support/callbacks.rb:414:in `_run__22188539__process_action__1016913818__callbacks'
activesupport (3.2.7) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.7) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.7) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.7) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.7) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.7) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.7) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.7) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.7) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.7) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.7) lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
activerecord (3.2.7) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.2.7) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.7) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.7) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.7) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.7) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.7) lib/action_dispatch/routing/route_set.rb:73:in `call'
actionpack (3.2.7) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
actionpack (3.2.7) lib/action_dispatch/routing/route_set.rb:36:in `call'
journey (1.0.4) lib/journey/router.rb:68:in `block in call'
journey (1.0.4) lib/journey/router.rb:56:in `each'
journey (1.0.4) lib/journey/router.rb:56:in `call'
actionpack (3.2.7) lib/action_dispatch/routing/route_set.rb:600:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.1) lib/rack/etag.rb:23:in `call'
rack (1.4.1) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.1) lib/rack/session/abstract/id.rb:205:in `context'
rack (1.4.1) lib/rack/session/abstract/id.rb:200:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/cookies.rb:338:in `call'
activerecord (3.2.7) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.7) lib/active_record/connection_adapters/abstract/connection_pool.rb:473:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.7) lib/active_support/callbacks.rb:405:in `_run__305680696__call__774818341__callbacks'
activesupport (3.2.7) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.7) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.7) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.7) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.7) lib/rails/rack/logger.rb:26:in `call_app'
railties (3.2.7) lib/rails/rack/logger.rb:16:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.1) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.1) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.7) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.1) lib/rack/lock.rb:15:in `call'
actionpack (3.2.7) lib/action_dispatch/middleware/static.rb:62:in `call'
railties (3.2.7) lib/rails/engine.rb:479:in `call'
railties (3.2.7) lib/rails/application.rb:220:in `call'
rack (1.4.1) lib/rack/content_length.rb:14:in `call'
railties (3.2.7) lib/rails/rack/log_tailer.rb:17:in `call'
rack (1.4.1) lib/rack/handler/webrick.rb:59:in `service'
c:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
c:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
c:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'