Rails Ancestry summing all nodes - ruby-on-rails-4

Question

I am using the Ancestry gem. Each node has a numerical value associated with it (:value). Each time I CRUD a node, I want to recalculate the whole tree so that each node ends up with the sum of the values of its children. (Leaf nodes stay unchanged.)
My controller actions contain this code to trigger the recalculation:
def create
...
#tree = Tree.new(tree_params)
if #tree.save
Tree.roots.each do |r|
recalc_tree(r)
end
redirect_to trees_url, notice: "Node was successfully created. " + note.to_s
else
render :new, notice: "There was an error saving this node. Please try again."
end
and in the private section at the bottom of the controller I have this custom helper method:
def recalc_tree(r)
total = 0
if r.has_children?
r.children.each do |c|
total = total + recalc_tree(c)
end
r.value = total
else
r.value
end
end
I don't get any errors in the browser (the node saves correctly) but neither does this update any of the values of the ancestor nodes.
I tried running the helper in the console but got an "undefined method" error:
>> helper.recalc_tree(Tree.roots.first)
Tree Load (0.0ms) SELECT "trees".* FROM "trees" WHERE "trees"."ancestry" IS NULL ORDER BY "trees"."id" ASC LIMIT 1
NoMethodError: undefined method `recalc_tree' for #<ActionView::Base:0x5fc82c0>
What am I doing wrongly?

Answer 1

The more rails-style way to do this is to use ActiveRecord's callback (http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html). Also since when a node is updated, only the updated node's ancestors will need to be updated, so we can save some CPU cycles by updating only ancestors along the path to the root.
Example:
class Tree < ActiveRecord::Base
after_save :update_ancestors
...
...
private
def update_ancestors
self.ancestors.each do |ancestor|
ancestor.value = ancestor.descendants.pluck(:value).sum
ancestor.save
end
end
end
I did not actually ran this code on my machine, but this is pretty much the direction to this problem!