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

  def scale(factor, auto_unit = false)
    if factor.present? && self.quantity.present? && factor != '1'
      self.quantity = UnitConversion.convert(self.quantity, factor, nil, nil)

      if auto_unit
        self.quantity, self.units = UnitConversion.auto_unit(self.quantity, self.units)
      end
    end
  end

end