Ruby do-loop to break down an array/hash - ruby-on-rails

Question

I made a self referring database using the has_many :through relationship:
**Product**
name
**Ingredient**
quantity
product_id
product_component_id
I can have an egg, carton of 12 eggs, and a flat of 16 cartons.
I am trying to write a loop that starts with a product and breaks down all the components of each product and those to the most basic state. The goal is to return an array of all the base products that go into any given product so the carton would return 12 eggs and the flat would return 192 Eggs.
I gave it a shot and this is how far I got:
def product_breakdown
results = []
ingredients.each do |ingredient|
if ingredient.product_component_id == nil
results += ingredient
else
Keep digging deeper?
end
end
return results
end
I am missing a whole concept when it comes to using the loop. If anyone has an advise on the name of the concepts that this requires, I would be very appreciative.
edit in order to be more clear I copied the relationships of the database.
class Product < ActiveRecord::Base
has_many :ingredients
has_many :product_components, :through => :ingredients
end
class Ingredient < ActiveRecord::Base
belongs_to :product
belongs_to :product_component, class_name: "Product", :foreign_key => "product_component_id"
end

Answer 1

I suggest using each_with_object to build the array. That way you don't even need the results variable, just return each_with_object's return value.
How do you differentiate between a unit, carton, and flat?

Answer 2

If I understand correctly, each ingredient has a component which can be nil, Carton, or Flat? And one carton always contains 12 units, and one flat 16 cartons? And a source, which is the type of ingredient (egg, milk, etc?)
In that case, I'd define a couple helper methods on Ingredient, an as_unit class method and a unit_quantity instance method:
def unit_quantity
case product_component_id
when nil
quantity
when CARTON_COMPONENT_ID
12 * quantity
when FLAT_COMPONENT_ID
192 * quantity
end
end
def self.as_unit ingredients
source_ids = ingredients.map(&:product_source_id).uniq
raise "Can't join different types together" if source_ids.count != 1
source_id = source_ids.first
quantity = ingredients.reduce(0) { |total, ingredient| total += ingredient.unit_quantity }
Ingredient.new quantity: quantity, product_component_id: nil, product_source_id: source_id
end
That way, you can rewrite products_breakdown to be:
def products_breakdown ingredients
ingredients.group_by(&:product_source_id).map do |_, ingredients|
Ingredient.as_unit ingredients
end
end
This should result in:
$ ingredients
#=> [<Ingredient: 3 Cartons of Egg>, <Ingredient: 2 Flats of Milk>, <17 Units of Egg>]
$ product_breakdown ingredients
#=> [<Ingredient: 53 Units of Egg>, <Ingredient: 384 Units of Milk>]
Is this at all what you were looking for? I'm not sure I fully understood your question...