ruby-on-rails - 为 Paperclip Imagemagick 调整大小提供变量字符串模型

Question

我正在使用回形针上传一些调整大小的图像。其中一种我想以五种方式之一进行裁剪......无论如何，我通过手动更改它们确定了要裁剪的字符串应该是什么样子，但现在我需要使其动态化，以便回形针可以基于裁剪用户想要什么...

问题是我得到了

undefined local variable or method `params' for #<Class:0x00000105b228d8>

我很确定这是因为我试图按照自己的意愿弯曲 rails 。无论如何，我认为我想要做的事情很清楚......只需将crop_geometry_thumb变量提供给convert_options......我实际上应该把这个逻辑放在哪里，我的模型将能够找到它？

class Asset < ActiveRecord::Base
   if  params[:crop_geometry] == "bottom"
     crop_geometry_thumb = "-crop 200x100+0+100 -scale 100x100"
   elsif  params[:crop_geometry] == "top"
     crop_geometry_thumb = "-crop 200x100+0+0 -scale 100x100"
   elsif  params[:crop_geometry] == "left"
     crop_geometry_thumb = "-crop 100x200+0+100 -scale 100x100"
   elsif  params[:crop_geometry] == "right"
     crop_geometry_thumb = "-crop 100x200+100+0 -scale 100x100"
   else
     crop_geometry_thumb = "-scale 100x100"
   end

  belongs_to :piece
  has_attached_file :asset, :styles => {
    :large => ['700x700', :jpg], 
    :medium => ['300x300>', :jpg], 
    :thumb => ["200x200>", :jpg]},
    :convert_options => {:thumb => crop_geometry_thumb}, ### supply a string from above... FAIL :(
    :path => ":id/:style/:filename",
    :storage => :s3,
    :s3_credentials => "#{RAILS_ROOT}/config/s3.yml",
    :s3_permissions => :private,
    :url => ':s3_domain_url'
end

Answer 1

因此，当前的问题是您的模型无法访问请求参数(即 params[:crop_geometry] )，只能访问您的 Controller + View 。

在某些情况下(尽管这从来都不是一个好主意)，您可以通过将 params 作为方法的参数传递给模型来绕过此 MVC 规则:

class FoosController < ApplicationController

  def action
     Foo.some_method(params)
  end
end

class Foo < ActiveRecord::Base

  some_method(params)
     puts params[:crop_geometry]
  end
end

相反，我建议将该参数信息传递到模型中定义的实例变量中，并将条件逻辑放入自定义 setter 方法中，如下所示:

class Asset < ActiveRecord::Base
  attr_reader :crop_geometry

  def crop_geometry=(crop_type)
    if  crop_type == "bottom"
     crop_string = "-crop 200x100+0+100 -scale 100x100"
    elsif  crop_type == "top"
      crop_geometry_thumb = "-crop 200x100+0+0 -scale 100x100"
    elsif  crop_type == "left"
      crop_geometry_thumb = "-crop 100x200+0+100 -scale 100x100"
    elsif  crop_type == "right"
      crop_geometry_thumb = "-crop 100x200+100+0 -scale 100x100"
    else
      crop_geometry_thumb = "-scale 100x100"
    end
    @crop_geometry = crop_geometry_thumb
  end
end

请注意，您必须更改表单，以便为 params[:asset][:crop_geometry] 分配“顶部”、“底部”或其他任何内容。

现在，要动态设置crop_geometry，您需要在has_attached_file 配置中使用lambda——这样每次访问配置时都会对其进行评估，而不仅仅是在最初加载模型时。干得好:

has_attached_file :asset, :styles => lambda {|attachment|
    :large => ['700x700', :jpg], 
    :medium => ['300x300>', :jpg], 
    :thumb => ["200x200>", :jpg]},
    :convert_options => {:thumb => attachment.instance.crop_geometry},
    :path => ":id/:style/:filename",
    ...
}

从 https://github.com/thoughtbot/paperclip 得到最后一部分(寻找“动态配置”)。