我在这个上画了一个空白。这是我的问题：
短版
我的image#create操作在image.save来电失败并投掷Undefined method "name" for nil:NilClass。 Image模型包括通过paperclip gem上传文件。
投掷我的部分：
只有在提交表单中包含:multipart => true时才会出现错误
当我拿出它时，表单完美无缺，当然图像文件没有上传。有关失败位置的详细信息，请参阅下面的堆栈跟踪。在尝试为INSERT语句引用某些内容时，它看起来像是一个零值，但我无法弄清楚是什么。我的控制器参数看起来没问题，我通过记录器检查以确保新的Image实例在它到达保存调用之前正确构建。
额外详情
我会尝试包含我能想到的所有细节，按重要性排序：
我正在使用paperclip并尝试通过S3进行存储，但是当我在我的图像模型中完全注释掉has_attached_file行时仍会出现此问题。
Image是Collection中的嵌套资源，它在to_param方法中以slug引用。
我有多租户系统的基础知识（又名Basecamp风格的用户子域，通过中心用户模型实现，范围涵盖所有组件）。
传递给控制器的参数
{"utf8"=>"✓",
"authenticity_token"=>"JYCMky7851j5cW4ChSWUCCL/02iePf6i/QWAgR8q5tE=",
"image"=>{"name"=>"My testerific image 2",
"slug"=>"my-testerific-image-2",
"description"=>"w",
"collection_id"=>"2",
"sort"=>"3",
"picture_file_name"=>#<ActionDispatch::Http::UploadedFile:0x00000101b3f540 @original_filename="David's pic 005.jpeg",
@content_type="image/jpeg",
@headers="Content-Disposition: form-data; name=\"image[picture_file_name]\"; filename=\"David's pic 005.jpeg\"\r\nContent-Type: image/jpeg\r\n",
@tempfile=#<File:/var/folders/df/mvsv5cs137gbyl8r7h428zp40000gn/T/RackMultipart20110814-64770-duz6wu>>},
"commit"=>"Create Image",
"collection_id"=>"my-new-collection"}
完整堆栈跟踪
activesupport (3.0.9) lib/active_support/whiny_nil.rb:48:in 'method_missing'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:20:in 'block in initialize'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'yield'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'default'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'block in initialize'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'yield'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'default'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'block in initialize'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'yield'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'default'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'block in initialize'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'yield'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'default'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:22:in 'block in initialize'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:63:in 'yield'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:63:in 'default'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:63:in 'accept'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:325:in 'block in dump_ivars'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:323:in 'each'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:323:in 'dump_ivars'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:85:in 'visit_Object'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:63:in 'accept'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:36:in '<<'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych.rb:165:in 'dump'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/psych/core_ext.rb:13:in 'psych_to_yaml'
activerecord (3.0.9) lib/active_record/connection_adapters/abstract/quoting.rb:34:in 'quote'
activerecord (3.0.9) lib/active_record/connection_adapters/sqlite3_adapter.rb:45:in 'quote'
arel (2.0.10) lib/arel/visitors/to_sql.rb:327:in 'quote'
arel (2.0.10) lib/arel/visitors/to_sql.rb:70:in 'block in visit_Arel_Nodes_Values'
arel (2.0.10) lib/arel/visitors/to_sql.rb:69:in 'map'
arel (2.0.10) lib/arel/visitors/to_sql.rb:69:in 'visit_Arel_Nodes_Values'
arel (2.0.10) lib/arel/visitors/visitor.rb:15:in 'visit'
arel (2.0.10) lib/arel/visitors/to_sql.rb:59:in 'visit_Arel_Nodes_InsertStatement'
arel (2.0.10) lib/arel/visitors/visitor.rb:15:in 'visit'
arel (2.0.10) lib/arel/visitors/visitor.rb:5:in 'accept'
arel (2.0.10) lib/arel/visitors/to_sql.rb:18:in 'block in accept'
activerecord (3.0.9) lib/active_record/connection_adapters/abstract/connection_pool.rb:111:in 'with_connection'
arel (2.0.10) lib/arel/visitors/to_sql.rb:16:in 'accept'
arel (2.0.10) lib/arel/tree_manager.rb:20:in 'to_sql'
arel (2.0.10) lib/arel/select_manager.rb:217:in 'insert'
activerecord (3.0.9) lib/active_record/relation.rb:14:in 'insert'
activerecord (3.0.9) lib/active_record/persistence.rb:274:in 'create'
activerecord (3.0.9) lib/active_record/timestamp.rb:47:in 'create'
activerecord (3.0.9) lib/active_record/callbacks.rb:277:in 'block in create'
activesupport (3.0.9) lib/active_support/callbacks.rb:414:in '_run_create_callbacks'
activerecord (3.0.9) lib/active_record/callbacks.rb:277:in 'create'
activerecord (3.0.9) lib/active_record/persistence.rb:250:in 'create_or_update'
activerecord (3.0.9) lib/active_record/callbacks.rb:273:in 'block in create_or_update'
activesupport (3.0.9) lib/active_support/callbacks.rb:429:in '_run_save_callbacks'
activerecord (3.0.9) lib/active_record/callbacks.rb:273:in 'create_or_update'
activerecord (3.0.9) lib/active_record/persistence.rb:40:in 'save'
activerecord (3.0.9) lib/active_record/validations.rb:43:in 'save'
activerecord (3.0.9) lib/active_record/attribute_methods/dirty.rb:21:in 'save'
activerecord (3.0.9) lib/active_record/transactions.rb:240:in 'block (2 levels) in save'
activerecord (3.0.9) lib/active_record/transactions.rb:292:in 'block in with_transaction_returning_status'
activerecord (3.0.9) lib/active_record/connection_adapters/abstract/database_statements.rb:139:in 'transaction'
activerecord (3.0.9) lib/active_record/transactions.rb:207:in 'transaction'
activerecord (3.0.9) lib/active_record/transactions.rb:290:in 'with_transaction_returning_status'
activerecord (3.0.9) lib/active_record/transactions.rb:240:in 'block in save'
activerecord (3.0.9) lib/active_record/transactions.rb:251:in 'rollback_active_record_state!'
activerecord (3.0.9) lib/active_record/transactions.rb:239:in 'save'
app/controllers/images_controller.rb:42:in 'block in create'
actionpack (3.0.9) lib/action_controller/metal/mime_responds.rb:264:in 'call'
actionpack (3.0.9) lib/action_controller/metal/mime_responds.rb:264:in 'retrieve_response_from_mimes'
actionpack (3.0.9) lib/action_controller/metal/mime_responds.rb:191:in 'respond_to'
app/controllers/images_controller.rb:40:in 'create'
actionpack (3.0.9) lib/action_controller/metal/implicit_render.rb:4:in 'send_action'
actionpack (3.0.9) lib/abstract_controller/base.rb:150:in 'process_action'
actionpack (3.0.9) lib/action_controller/metal/rendering.rb:11:in 'process_action'
actionpack (3.0.9) lib/abstract_controller/callbacks.rb:18:in 'block in process_action'
activesupport (3.0.9) lib/active_support/callbacks.rb:451:in '_run__867212960703161301__process_action__2360218484576085785__callbacks'
activesupport (3.0.9) lib/active_support/callbacks.rb:410:in '_run_process_action_callbacks'
activesupport (3.0.9) lib/active_support/callbacks.rb:94:in 'run_callbacks'
actionpack (3.0.9) lib/abstract_controller/callbacks.rb:17:in 'process_action'
actionpack (3.0.9) lib/action_controller/metal/instrumentation.rb:30:in 'block in process_action'
activesupport (3.0.9) lib/active_support/notifications.rb:52:in 'block in instrument'
activesupport (3.0.9) lib/active_support/notifications/instrumenter.rb:21:in 'instrument'
activesupport (3.0.9) lib/active_support/notifications.rb:52:in 'instrument'
actionpack (3.0.9) lib/action_controller/metal/instrumentation.rb:29:in 'process_action'
actionpack (3.0.9) lib/action_controller/metal/rescue.rb:17:in 'process_action'
actionpack (3.0.9) lib/abstract_controller/base.rb:119:in 'process'
actionpack (3.0.9) lib/abstract_controller/rendering.rb:41:in 'process'
actionpack (3.0.9) lib/action_controller/metal.rb:138:in 'dispatch'
actionpack (3.0.9) lib/action_controller/metal/rack_delegation.rb:14:in 'dispatch'
actionpack (3.0.9) lib/action_controller/metal.rb:178:in 'block in action'
actionpack (3.0.9) lib/action_dispatch/routing/route_set.rb:62:in 'call'
actionpack (3.0.9) lib/action_dispatch/routing/route_set.rb:62:in 'dispatch'
actionpack (3.0.9) lib/action_dispatch/routing/route_set.rb:27:in 'call'
rack-mount (0.6.14) lib/rack/mount/route_set.rb:148:in 'block in call'
rack-mount (0.6.14) lib/rack/mount/code_generation.rb:93:in 'block in recognize'
rack-mount (0.6.14) lib/rack/mount/code_generation.rb:68:in 'optimized_each'
rack-mount (0.6.14) lib/rack/mount/code_generation.rb:92:in 'recognize'
rack-mount (0.6.14) lib/rack/mount/route_set.rb:139:in 'call'
actionpack (3.0.9) lib/action_dispatch/routing/route_set.rb:493:in 'call'
warden (1.0.5) lib/warden/manager.rb:35:in 'block in call'
warden (1.0.5) lib/warden/manager.rb:34:in 'catch'
warden (1.0.5) lib/warden/manager.rb:34:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/best_standards_support.rb:17:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/head.rb:14:in 'call'
rack (1.2.3) lib/rack/methodoverride.rb:24:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/params_parser.rb:21:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/flash.rb:182:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/session/abstract_store.rb:149:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/cookies.rb:302:in 'call'
activerecord (3.0.9) lib/active_record/query_cache.rb:32:in 'block in call'
activerecord (3.0.9) lib/active_record/connection_adapters/abstract/query_cache.rb:28:in 'cache'
activerecord (3.0.9) lib/active_record/query_cache.rb:12:in 'cache'
activerecord (3.0.9) lib/active_record/query_cache.rb:31:in 'call'
activerecord (3.0.9) lib/active_record/connection_adapters/abstract/connection_pool.rb:354:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/callbacks.rb:46:in 'block in call'
activesupport (3.0.9) lib/active_support/callbacks.rb:416:in '_run_call_callbacks'
actionpack (3.0.9) lib/action_dispatch/middleware/callbacks.rb:44:in 'call'
rack (1.2.3) lib/rack/sendfile.rb:107:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/remote_ip.rb:48:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/show_exceptions.rb:47:in 'call'
railties (3.0.9) lib/rails/rack/logger.rb:13:in 'call'
rack (1.2.3) lib/rack/runtime.rb:17:in 'call'
activesupport (3.0.9) lib/active_support/cache/strategy/local_cache.rb:72:in 'call'
rack (1.2.3) lib/rack/lock.rb:11:in 'block in call'
<internal:prelude>:10:in 'synchronize'
rack (1.2.3) lib/rack/lock.rb:11:in 'call'
actionpack (3.0.9) lib/action_dispatch/middleware/static.rb:30:in 'call'
railties (3.0.9) lib/rails/application.rb:168:in 'call'
railties (3.0.9) lib/rails/application.rb:77:in 'method_missing'
railties (3.0.9) lib/rails/rack/log_tailer.rb:14:in 'call'
rack (1.2.3) lib/rack/content_length.rb:13:in 'call'
rack (1.2.3) lib/rack/handler/webrick.rb:52:in 'service'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/webrick/httpserver.rb:111:in 'service'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/webrick/httpserver.rb:70:in 'run'
/Users/daw/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/webrick/server.rb:183:in 'block in start_thread'
根据要求，型号代码：
class Image < ActiveRecord::Base
belongs_to :collection
belongs_to :user
before_save :create_slug
has_attached_file :picture,
#:styles => {
# :thumb => '100x100>',
# :full => '800x800>'
#},
:storage => :s3,
:s3_credentials => Rails.root.join( 'config', 's3.yml' ),
:path => ":id/:style/:filename"
def to_param
self.name.parameterize
end
private
def create_slug
self.slug = self.to_param
end
end
我将使用Image构建的:multipart => true实例与没有它的实例进行了比较，并确认唯一的区别是文件上传字段picture_file_name。没有:multipart => true，它是一个带文件名的字符串（不足为奇）。有了它，它就是ActionDispatch::Http::UploadedFile的一个实例。鉴于堆栈跟踪显示在to_yaml调用期间失败，可能问题在于UploadedFile实例转换为YAML？
答案 0 :(得分：7)
好吧，我终于屈服了，通过记录器输出跟踪了我的ActiveRecord源代码。事实证明，正如我所怀疑的那样，它无法保存UploadedFile，因为它无法将其转换为YAML。
然而，这是因为我犯了一个愚蠢的错误。在我的提交表格中，我有：
<%= f.file_field :picture_file_name %>
应该是：
<%= f.file_field :picture %>
paperclip gem知道:picture是上传的文件，并使用背景魔法将文件名保存到正确的字段。我只是低估了我的易用性！
通常情况下，我会删除这个微不足道的问题，但看到我犯了这个错误，其他人可能会在将来，并且很少有人指出我的解决方案。所以我会继续帮助将来搜索类似密集的开发人员！
答案 1 :(得分：1)
经过大量的搜索和调试。这个问题的主要症状是带有文件字段的表单被制作为多部分表单而rails 3.2无法保存数据，因为它试图保存数据库中不存在的其他参数（文件的归档）对象）。
获取适当的值并将它们保存到某个变量并从params中删除文件哈希似乎解决了这个问题！
以下是使用rails 3.2
保存在数据库中的工作代码示例file = params[:document][:file].tempfile.read
params[:document].delete(:file)
@document = Document.new(params[:document])
respond_to do |format|
if @document.save
@document.file = file
@document.save
format.html { redirect_to @document, notice: 'Document was successfully created.' }
format.json { render json: @document, status: :created, location: @document }
else
format.html { render action: "new" }
format.json { render json: @document.errors, status: :unprocessable_entity }
end
end
答案 2 :(得分：0)
您没有发布，但我认为您应该在表单中使用:html => { :multipart => true }而不只是:multipart => true，例如：
form_for object, :html => { :multipart => true } do |o|
...
答案 3 :(得分：0)
即使我有正确的字段，我也花了大约一个星期来处理相同的错误。
导致我所有头痛的愚蠢只是视图中标签的顺序。
导致错误
NoMethodError in DatenightsController#create undefined methodname' for nil:NilClass：
<%= f.file_field :photo %>
<%= f.text_field :name %>
以上引用错误的解决方案（这里的序列/顺序很重要）
<%= f.text_field :name %>
<%= f.file_field :photo %>
由于这个问题耗费了我很多甜蜜的时间，我认为这对你有帮助。