Place in db directory and run via plain `ruby`

list_user_and_person_fks.rb

module ActiveRecord
  class Schema
    attr_reader :users, :people

    def initialize
      @people = []
      @users = []
    end

    def self.define(*args, &block)
      a = new
      a.instance_eval(&block)
      puts "=== User references ==="
      puts a.users
      puts
      puts "=== Person references ==="
      puts a.people
      puts
    end

    class Table
      attr_reader :person, :user

      def initialize
        @user = false
        @person = false
      end

      def method_missing(method, *args)
        @user ||= (args.first == 'user_id')
        @person ||= (args.first == 'person_id')
      end
    end

    def create_table(name, *args)
      t = Table.new
      yield t
      @users << name if t.user
      @people << name if t.person
    end

    def method_missing(method, *args); end
  end
end

require_relative './schema.rb'