我想添加图片作为评论的附件。评论属于帖子。我看过this要点。我也试过使用nested_form gem，但仍然是同样的错误。
形式
<%= semantic_form_for([@post, @comment], validate: true, html: {multipart: true}, 'data-update-target' => 'comments', class: 'comments') do |f| %>
<%= f.text_field :title %>
<%= f.semantic_fields_for :comment_images do |pic| %>
<%= pic.inputs do %>
<%= pic.hidden_field :id %>
<%= pic.hidden_field :attachable_id %>
<%= pic.hidden_field :attachable_type %>
<%= pic.file_field :image %>
<% end %>
<% end %>
...
comment_image模型
class CommentImage < ActiveRecord::Base
belongs_to :attachable, polymorphic: true
attr_accessible :image, :attachable_id, :attachable_type
mount_uploader :image, ImageUploader
end
评论模型
class Comment < ActiveRecord::Base
attr_accessor :image, :file
has_many :comment_images, :as => :attachable, :dependent => :destroy
accepts_nested_attributes_for :comment_images, :allow_destroy => true
服务器日志
Started GET "/posts/1/comments/new" for ....136 at 2014-04-28 16:41:47 +0000
Processing by CommentsController#new as HTML
Parameters: {"post_id"=>"1"}
Post Load (0.3ms) SELECT "posts".* FROM "posts" WHERE "posts"."id" = ? LIMIT 1 [["id", "1"]]
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1 [["id", 2]]
params********************{"action"=>"new", "controller"=>"comments", "post_id"=>"1"}
Completed 500 Internal Server Error in 9ms
NoMethodError - undefined method `[]' for nil:NilClass:
activerecord (4.0.4) lib/active_record/attribute_methods/read.rb:86:in `block in read_attribute'
activerecord (4.0.4) lib/active_record/attribute_methods/read.rb:84:in `read_attribute'
activerecord (4.0.4) lib/active_record/attribute_methods.rb:344:in `[]'
activerecord (4.0.4) lib/active_record/associations/association_scope.rb:73:in `block in add_constraints'
activerecord (4.0.4) lib/active_record/associations/association_scope.rb:44:in `add_constraints'
activerecord (4.0.4) lib/active_record/associations/association_scope.rb:19:in `scope'
activerecord (4.0.4) lib/active_record/associations/association.rb:103:in `association_scope'
activerecord (4.0.4) lib/active_record/associations/association.rb:87:in `scope'
activerecord (4.0.4) lib/active_record/associations/collection_association.rb:382:in `scope'
activerecord (4.0.4) lib/active_record/associations/collection_proxy.rb:37:in `initialize'
activerecord (4.0.4) lib/active_record/relation/delegation.rb:78:in `new'
activerecord (4.0.4) lib/active_record/associations/collection_association.rb:37:in `reader'
activerecord (4.0.4) lib/active_record/associations/builder/association.rb:70:in `comment_images'
app/controllers/comments_controller.rb:18:in `new'
actionpack (4.0.4) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.0.4) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.0.4) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.0.4) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (4.0.4) lib/active_support/callbacks.rb:433:in `_run__1580909207748771124__process_action__callbacks'
activesupport (4.0.4) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.4) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (4.0.4) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.0.4) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.0.4) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.4) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.4) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.4) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.0.4) lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
activerecord (4.0.4) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.0.4) lib/abstract_controller/base.rb:136:in `process'
actionpack (4.0.4) lib/abstract_controller/rendering.rb:44:in `process'
actionpack (4.0.4) lib/action_controller/metal.rb:195:in `dispatch'
actionpack (4.0.4) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.0.4) lib/action_controller/metal.rb:231:in `block in action'
actionpack (4.0.4) lib/action_dispatch/routing/route_set.rb:80:in `dispatch'
actionpack (4.0.4) lib/action_dispatch/routing/route_set.rb:48:in `call'
actionpack (4.0.4) lib/action_dispatch/journey/router.rb:71:in `block in call'
actionpack (4.0.4) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.0.4) lib/action_dispatch/routing/route_set.rb:674:in `call'
omniauth (1.2.1) lib/omniauth/strategy.rb:186:in `call!'
omniauth (1.2.1) lib/omniauth/strategy.rb:164:in `call'
omniauth (1.2.1) lib/omniauth/builder.rb:59:in `call'
meta_request (0.3.0) lib/meta_request/middlewares/app_request_handler.rb:13:in `call'
rack-contrib (1.1.0) lib/rack/contrib/response_headers.rb:17:in `call'
meta_request (0.3.0) lib/meta_request/middlewares/headers.rb:16:in `call'
meta_request (0.3.0) lib/meta_request/middlewares/meta_request_handler.rb:13:in `call'
newrelic_rpm (3.8.0.218) lib/new_relic/rack/error_collector.rb:55:in `call'
newrelic_rpm (3.8.0.218) lib/new_relic/rack/agent_hooks.rb:32:in `call'
newrelic_rpm (3.8.0.218) lib/new_relic/rack/browser_monitoring.rb:27:in `call'
rack (1.5.2) lib/rack/etag.rb:23:in `call'
rack (1.5.2) lib/rack/conditionalget.rb:25:in `call'
rack (1.5.2) lib/rack/head.rb:11:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/flash.rb:241:in `call'
rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/cookies.rb:486:in `call'
activerecord (4.0.4) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.0.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
activerecord (4.0.4) lib/active_record/migration.rb:373:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.4) lib/active_support/callbacks.rb:373:in `_run__2395107169417203351__call__callbacks'
activesupport (4.0.4) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.4) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
better_errors (1.1.0) lib/better_errors/middleware.rb:84:in `protected_app_call'
better_errors (1.1.0) lib/better_errors/middleware.rb:79:in `better_errors_call'
better_errors (1.1.0) lib/better_errors/middleware.rb:56:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.4) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.4) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.0.4) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.0.4) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.0.4) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.0.4) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.2) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.4) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/static.rb:64:in `call'
rack (1.5.2) lib/rack/sendfile.rb:112:in `call'
railties (4.0.4) lib/rails/engine.rb:511:in `call'
railties (4.0.4) lib/rails/application.rb:97:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service'
/home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
/home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
/home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'
答案 0 :(得分：0)
问题在于
attr_accessible :image, :attachable_id, :attachable_type
我有'protected_attributes'宝石，但我仍然需要使用strong_parameters创建控制器，以使其工作。更多信息here。