How to make a multi-level category model?

Question

MySQL

The task is to create a category model (name, description) - this is not a problem. The question is how to create a relationship between the two categories "Parent"->"Child". At the same time, make multi-level categories, for example
Clothing
- Children's clothing
- hats
- shoes
- Women's clothing
- Sweatshirts
, etc.

Answer 1

For example, a model where there is a parent_id pointing to the parent (for root it is nil)

class Category < ActiveRecord::Base
  has_closure_tree
  acts_as_tree
end

+ gem closure_tree

Answer 2

https://www.ruby-toolbox.com/categories/Active_Rec...
awesome-ruby.com/ (Tree: Ancestry ...)

Answer 3

Alternatively:
You have your global category model which has_many some private categories. They, in turn, have_many already specific goods.