Goal: Convert entire hierarchy of models into tree in 1 database call, such that you can loop through them depth-first

awesome_nested_set_optimization_helper.rb

def simple_nested_set(clazz) # Post for example
  stack = [] # Post for example
  result = []
  clazz.all(:order => "lft").each do |node|
    if stack.empty?
      stack.push({:node => node, :children => []})
      result << stack.last
      next
    end
    if stack.last[:node].lft < node.lft && node.lft < stack.last[:node].rgt
      child = {:node => node, :children => []}
      stack.last[:children] << child
      if node.rgt + 1 == stack.last[:node].rgt
        stack.pop
      end
      unless node.leaf? # (node.rgt - node.lft == 1)
        stack.push(child)
      end
    else
      stack.pop
    end
  end

  result
end

Inside each suggestion:

      stack.pop while stack.any? && node.lft > stack.last[:node].rgt
      child = {node: node, children: []}
      (stack.empty? ? result : stack.last[:children]) << child
      stack << child