app/models/spree/product_decorator.rb
module Spree
module ProductDecorator
def self.prepended(base)
base.has_many :product_uploads, class_name: 'Spree::ProductUpload', dependent: :destroy
base.has_many :uploads, through: :product_uploads, class_name: 'Spree::Upload', source: :upload
end
end
Product.prepend(ProductDecorator)
end