在ActiveSupport :: Concern模块中访问模型属性

Question

I have some models which share the same functionality just on other paths. So I decided to put these methods in a module and set the path in the model. My problem is that I'm not able to access the attribute in my module.

model:

class Job < ActiveRecord::Base
  include ImageModel

  image_dir = "jobs"
end

module:

module ImageModel
  extend ActiveSupport::Concern

  def delete_image
      unless pic_link == "" || pic_link == nil
        begin
          if File.delete(Rails.root.join("public", "images", image_dir, pic_link))
            return true
          else
            return false
          end
        rescue
          return true #an error occured but when the image does not exist we still return true
        end
      end

      return true
    end

    def replace_image(new_image)
      File.open(Rails.root.join("public", "images", image_dir, new_image.original_filename), "wb") do |f|
        if f.write new_image.read
          delete_image
          pic_link = new_image.original_filename
          return true #everything went fine
        else
          return false #return false if new image could not be written
        end
      end
    end
end

The error i get:

undefined local variable or method `image_dir' for #<Job:0x007f8a93b9e8d8>

on this line:

File.open(Rails.root.join("public", "images", image_dir, new_image.original_filename), "wb") do |f|

Did I miss something or did I oversee something important?

Felix

Answer 1

I think the design of module still have room to improve. But for this specific question, here is the quickfix.

class Job < ActiveRecord::Base
  include ImageModel

  def image_dir
    "jobs"
  end
end

Answer 2

You should define your image_dir = "jobs" in the module itself. because you are including your module in your model, and your module is not able to get the declaration, you have done in your model.

Or you can change your delete_image method to take parameters :

def delete_image(image_dir)
      unless pic_link == "" || pic_link == nil
        begin
          if File.delete(Rails.root.join("public", "images", image_dir, pic_link))
            return true
          else
            return false
          end
        rescue
          return true #an error occured but when the image does not exist we still return true
        end
      end

      return true
    end

and where you are calling that method, pass an argument like this:

 delete_image("jobs")

same in the case of replace_image method:

 def replace_image(new_image, image_dir)
      File.open(Rails.root.join("public", "images", image_dir, new_image.original_filename), "wb") do |f|
        if f.write new_image.read
          delete_image
          pic_link = new_image.original_filename
          return true #everything went fine
        else
          return false #return false if new image could not be written
        end
      end
    end

Hope it will help. Thanks