parsley/app/models/recipe_ingredient.rb

class RecipeIngredient < ActiveRecord::Base

  belongs_to :ingredient
  belongs_to :recipe, inverse_of: :recipe_ingredients

  validates :sort_order, presence: true
  validates :custom_density, density: true, allow_blank: true

  def custom_name
    if self.ingredient_id.present?
      self.ingredient.name
    else
      super
    end
  end

  def custom_density
    if self.ingredient_id.present?
      self.ingredient.density
    else
      super
    end
  end

end