这似乎是Rails 4的一个错误，它适用于Rails 3，但是4.1和4.2都失败了。我创建了一个新的测试项目，使用单个模型Post，然后添加了一个Paperclip文件字段，称为avatar。顺便提一下Paperclip 4.2.1。
这是我的测试模型，它只验证内容类型。
class Post < ActiveRecord::Base
has_attached_file :avatar
validates_attachment_content_type :avatar, :content_type => ["image/jpg", "image/jpeg", "image/png", "image/gif"]
end
控制器
class PostsController < ApplicationController
#...
# Just as generated by Rails, except as below, where I added the avatar field:
# Never trust parameters from the scary internet, only allow the white list through.
def post_params
params.require(:post).permit(:name, :body, :avatar)
end
end
_form视图
<%= form_for(@post, :url => posts_path, :html => { :multipart => true }) do |f| %>
...Several lines generated by Rails
<div class="field">
<%= f.label :body %><br>
<%= f.file_field :avatar %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
尝试上传图片会产生此错误：
NoMethodError (undefined method `split' for nil:NilClass):
paperclip (4.2.1) lib/paperclip/media_type_spoof_detector.rb:63:in `type_from_file_command'
paperclip (4.2.1) lib/paperclip/media_type_spoof_detector.rb:50:in `calculated_content_type'
paperclip (4.2.1) lib/paperclip/media_type_spoof_detector.rb:42:in `calculated_media_type'
paperclip (4.2.1) lib/paperclip/media_type_spoof_detector.rb:30:in `media_type_mismatch?'
paperclip (4.2.1) lib/paperclip/media_type_spoof_detector.rb:13:in `spoofed?'
paperclip (4.2.1) lib/paperclip/validators/media_type_spoof_detection_validator.rb:8:in `validate_each'
activemodel (4.2.0) lib/active_model/validator.rb:151:in `validate'
org/jruby/RubyArray.java:1613:in `each'
activemodel (4.2.0) lib/active_model/validator.rb:148:in `validate'
paperclip (4.2.1) lib/paperclip/validators.rb:68:in `create_validating_before_filter'
我蠢蠢欲动。在... \ gems \ paperclip-4.2.1 \ lib \ paperclip \ helpers中，有一个使用此方法的模块：
def run(cmd, arguments = "", interpolation_values = {}, local_options = {})
command_path = options[:command_path]
Cocaine::CommandLine.path = [Cocaine::CommandLine.path, command_path].flatten.compact.uniq
if logging? && (options[:log_command] || local_options[:log_command])
local_options = local_options.merge(:logger => logger)
end
Cocaine::CommandLine.new(cmd, arguments, local_options).run(interpolation_values)
end
似乎偶然发现了最后一行，似乎是因为它正在寻找错误的文件。以下是参数：
Parameters: {"utf8"=>"?", "authenticity_token"=>"gYTVjpqNjHpzZt5aBdpWzHhwZ3V0URFhH/TkRQT5P6qJShmFuauehEdRXtGiNZoSmPmPK5q+F7jOv8VR3B6hTg==", "post"=>{"name"=>"name", "body"=>"body...", "avatar"=>#<ActionDispatch::Http::UploadedFile:0x86dbbe @original_filename="colour test.png", @headers="Content-Disposition: form-data; name=\"post[avatar]\"; filename=\"colour test.png\"\r\nContent-Type: image/png\r\n", @tempfile=#<Tempfile:C:\Users\user\AppData\Local\Temp\RackMultipart20150422-7116-12wd99n.png>, @content_type="image/png">}, "commit"=>"Create Post"}
请注意，临时文件启动“RackMultipart”（在Rails 4执行其强参数之后，它仍然存在）。然而，可卡因正在发送：
file -b --mime "C:\Users\user\AppData\Local\Temp\7f220723ebddeeb3a4feff6ec43c42a5150422-7116-1et5e2r-.png"
RackMultipart文件存在，Concaine正在寻找的文件没有。毫不奇怪，它是对象，说“bin / rails：没有这样的文件或目录 - ”并返回nil，因此返回错误。
顺便说一下，我知道这个问题，但我认为这是一个不同的问题，因为这是Paperclip中的一个错误，显然在2012年解决了（尽管我在Windows 7上）。 Paperclip on Windows - undefined method `split' for nil:NilClass