product_image.rb

class ProductImage < ActiveRecord::Base
  attr_accessible :name, :product_id, :path

  belongs_to :product
  has_many :product_option_value_images
  has_many :product_option_values, through: :product_option_value_images

  def getImage(options)
    if(options.empty? == false)
  		image = ProductImage.joins(:product_option_values).where(product_option_values: { id: options })
  		image
  	end
  end

end

product_option_value.rb

class ProductOptionValue < ActiveRecord::Base
  attr_accessible :option_value_id, :price, :product_id

  belongs_to :product
  belongs_to :option_value

end

product_option_value_image.rb

class ProductOptionValueImage < ActiveRecord::Base
  attr_accessible :product_image_id, :product_option_value_id
  
  belongs_to :product_option_value
  belongs_to :product_image
  
end