如果你使用fog，你可以这样做：

has_attached_file :report,
  fog_file: lambda { |attachment|
    {
      content_type: 'text/csv',
      content_disposition: "attachment; filename=#{attachment.original_filename}",
    }
  }

如果您使用Amazon S3作为您的存储提供商，则应该可以使用以下内容：

has_attached_file :report
  s3_headers: lambda { |attachment|
    { 
      'Content-Type' => 'text/csv',
      'Content-Disposition' => "attachment; filename=#{attachment.original_filename}",
    }
  }

最近遇到了这个问题，post进程和lambda都不工作，所以做了一个工作。与其他观察一样，当调用s3 lambda头时，附件的值为空。
1.将此线添加到模型中

attr_accessor :tmp_content_type, :tmp_file_name

1.覆盖文件赋值方法，这样我们就可以获取文件信息并将其存储以备后用

def file=(f)
  set_tmp_values(f.path)
  file.assign(f)
end

def set_tmp_values(file_path)
  self.tmp_file_name = File.basename(file_path)
  self.tmp_content_type = MIME::Types.type_for(file_path).first.content_type
end

1.使用临时变量

:s3_headers => lambda { |attachment|
  {
    'Content-Type' => attachment.tmp_content_type,
    "Content-Disposition" => "attachment; filename=\"# {attachment.tmp_file_name}\""
  }
}

我正在使用Paperclip 6.1.0和Rails 5.2.3，Ruby 2.6.6，这个答案使用了James Euangel在现有答案中提出的相同想法，但它更通用，并使用了猴子补丁。
我将在使用Paperclip::Attachment作为文件附件的模型上定义attr_accessors，并使用它们来设置传递给has_attached_file宏的s3_headers选项中的值。

# app/models/concerns/paperclip_attributes_maker.rb
# This concern defines attr_accessors for the paperclip attachment attributes of the ActiveRecord model

module PaperclipAttributesMaker
  extend ActiveSupport::Concern

  def self.included
    base.class_eval do
      base::PAPERCLIP_ATTACHMENT_ATTRS.each do |attachment_attr|
        attr_accessor "paperclip_#{attachment_attr}_content_type"
        attr_accessor "paperclip_#{attachment_attr}_filename"
      end
    end
  end
end

现在，我们需要对Paperclip::HasAttachaedFile类中定义的附件setter方法进行monkey-patch：

# app/initializers/patch_paperclip_has_attached_file.rb
# it patches paperclip/has_attached_file.rb

module Paperclip
  class HasAttachedFile
    def define_setter
      name = @name
      @klass.send :define_method, "#{@name}=" do |file|
        content_type = (file.content_type || MIME::Types.type_for(file.path).first.content_type) rescue nil
        instance_variable_set("@paperclip_#{name}_content_type", content_type)
        instance_variable_set("@paperclip_#{name}_filename", (file.original_filename rescue nil))
        send(name).assign(file)
      end
    end
  end
end

最后，我们声明Paperclip附件（我的意思是我们在ActiveRecord模型中得到了多少附件）：

class StudentAttachment < ApplicationRecord
  PAPERCLIP_ATTACHMENT_ATTRS = [:attachment1, :attachment2]
  
  include PaperclipAttributesMaker # should be included after definition of PAPERCLIP_ATTACHMENT_ATTRS
  
  #...other code

  has_attached_file :attachment1, { # other options here
    s3_headers: lambda { |attachment|
      {
        'Content-Type' => attachment.paperclip_attachment1_content_type,
        "Content-Disposition" => "attachment; filename=\"#{attachment.paperclip_attachment1_filename}\""}}
      }

  has_attached_file :attachment2, { # other options here
    s3_headers: lambda { |attachment|
      {
        'Content-Type' => attachment.paperclip_attachment2_content_type,
        "Content-Disposition" => "attachment; filename=\"#{attachment.paperclip_attachment2_filename}\""}}
      }
end