taras2358

# frozen_string_literal: true

class Array
  module Mixins
    # Mixing for providing flatten method into Array
    module Flatten
      # Returns a flatten copy of array
      # Example: [[1,2,[3]],4].recursive_flatten => [1, 2, 3, 4]
      def recursive_flatten(result: [])
        each do |element|

taras2358

Given you have Rails e-commerce website. There are Product and Category models which have has_and_belongs_to_many relationship.

models/product.rb

class Product
  has_and_belongs_to_many :categories
end

models/category.rb