ruby on rails - Ingredient has many sub-ingredients modelling -

i've got recipe model, , ingredient model. right recipe has_and_belongs_to_many :ingredients , ingredient has_and_belongs_to_many :recipes.

because ingredient conceivably made of other ingredients, i'm trying self-join on model, so:

has_many :components, class_name: 'ingredient', foreign_key: 'parent_id' belongs_to :parent,   class_name: 'ingredient' 

now, works, each ingredient can have 1 parent, e.g., mayonnaise in "crab cakes" ingredient part of recipe, can't ingredient in "spicy mayo" ingredient of other recipe simultaneously.

what i'm trying interface this:

r = recipe.create(name: "jumbo lump crab cakes") r.ingredients << ingredient.create(name: "crab cakes") r.ingredients[0].ingredients # => [] r.ingredients[0].ingredients.create(name: "mayonnaise") r.ingredients[0].ingredients # => [#<ingredient id: 2, name: "mayonnaise">] r.ingredients[0].ingredients[0].ingredients.create(name: "eggs") r.ingredients[0].ingredients[0].ingredients # => [#<ingredient id: 3, name: "eggs">]  ingredient.last               # => #<ingredient id: 3, name: "eggs"> ingredient.last.parent        # => #<ingredient id: 2, name: "mayonnaise"> ingredient.last.parent.parent # => #<ingredient id: 1, name: "crab cakes">  # bonus points if child ingredient can "walk up" heritage tree recipe: ingredient.last.recipe        # => #<recipe id: 1> 

obviously need association table store ingredient/sub-ingredient relationships, that's far i've figured out. i've tried various feats of source , through wizardry no luck.

i messed around polymorphic association, has parent , it's either of type ingredient or of type recipe, couldn't work out interface wanted.

think got figured out. ended using modified version of this post.

create_table :ingredients |t| # :hunts   t.references :parent # :predator   t.references :child  # :prey end  add_index :ingredients, :parent_id # :hunts, :predator_id add_index :ingredients, :child_id  # :hunts, :prey_id  create_table :components |t| # :animals   t.string :name end  class component < activerecord::base # animal   has_many :parentage, foreign_key: 'parent_id',                        class_name: 'ingredient',                        dependent: :destroy    has_many :children, through: :parentage    has_many :progeny, foreign_key: 'child_id',                      class_name: 'ingredient',                      dependent: :destroy    has_many :parents, through: :progeny end  class ingredient < activerecord::base # hunt   belongs_to :parent, class_name: 'component'   belongs_to :child,  class_name: 'component' end 

fairly happy parentage/progeny naming.