Question

I am trying to fetch self-referential data from Rails. I have a model called Task with the following code:

class Task < ActiveRecord::Base
  has_many :tasks
  has_many :relationships, foreign_key: "follower_id", dependent: :destroy
  has_many :followed_tasks, through: :relationships, source: :followed
  scope :orphans, :conditions => "id NOT IN (SELECT DISTINCT followed_id FROM relationships)"

In my controller I would like to get all of the tasks with their children (subtasks) and grandchildren.
So far I have been doing this:

@tasks = Task.orphans.to_json(:include => { :followed_tasks => {
:include => :followed_tasks}})

That is probably not the most efficient way but it is one that I could come up with that works. Now if I want to have more levels of nesting this code quickly becomes hard to maintain. How could I improve my code to be able to specify a variable like maxLevelsNum = 4 and then have my query somehow fetch tasks with their subtasks four levels deep?

Answer 1

It’s been a while since the question was asked, but, you can find below a possible answer (maxLevelsNum needs to be greater or equal to 1):

hash_string = constructHash(maxLevelsNum)

def constructHash(treeDepth)
  output = ":include => :followed_tasks"

  (2..treeDepth).each do 
    output = ":include => { :followed_tasks => {" + output + "}}"
  end

  return "{" + output + "}"
end

@tasks = Task.orphans.to_json(eval(hash_string))