associations.rb

class Ingredient
  has_many :doses
  belongs_to :alcohol
end

class Dose
  belongs_to :ingredient
  belongs_to :cocktail
end

class Cocktail
  has_many :doses
  has_many :ingredients, through: :doses
  has_many :alcohols, through: :ingredients
end

class Alcohol
  has_many :ingredients
end

ice = Ingredient.create(name: "ice")

cocktail = Cocktail.create(name: "mojito")

dose = Dose.new(description: "25ml", cocktail: cocktail, ingredient: ice)


cocktail.doses

cocktail.ingredients

# Cocktail has many ingredients
cocktail.dose.map do |dose|
  dose.ingredient
end

# Cocktail has_many alcohols
cocktail.ingredients.map do |ingredient|
  ingredient.alcohol
end