How do I validate the dimensions of attached files given this set up? I have Promotion Model which has a 'has_one' association with the Promotion_Attachment Model. The Promotion_Attachment Model manages a few attached files. I want to be able to validate the dimensions of each uploaded image file upon creation. I'm having trouble figuring out th…

gistfile1.rb

class PromotionAttachment < ActiveRecord::Base
  belongs_to :promotion

	attr_accessible \
	:like_gate_image,
	:promotion_image,
  	:app_icon,
	:video_url
	
	
	validate :like_gate_image_dimensions
	
	# If ENABLE_S3 returns TRUE (config/initializers/_tmg.rb) then files will be sent to s3 otherwise they will be stored locally
	if ENABLE_S3
	  [:like_gate_image, :promotion_image].each do |file_name|
		  class_eval do
		    has_attached_file file_name,
		      { styles:
		        { medium: "300x300>}",
		          thumb: "100x100>"
		        },
		        storage: :s3,
		        s3_credentials: "#{::Rails.root}/config/aws.yml",
		        path: ":attachment/:id/:style.:extension",
		      }
		  end
	  end
	else
		[:like_gate_image, :promotion_image].each do |file_name|
		  class_eval do
		    has_attached_file file_name,
		      { styles:
		        { medium: "300x300>}",
		          thumb: "100x100>"
		        },
		        :url => "/system/:attachment/:id/:style.:extension",
		      }
		  end
	  end
	end
  
   def like_gate_image_dimensions #i'd like to be able to check that a like_gate_image meets the right dimensions
    dimensions = Paperclip::Geometry.from_file(file.queued_for_write[:original].path)
    self.width = dimensions.width
    self.height = dimensions.height
    if dimensions.width != 810 && dimensions.height > 200
      errors.add(:like_gate_image,'width must be equal to 810px, and the height must be atleast 200px.')
    end
  end
  
end