Need array of self, children and children childrens in rails - mysql

Question

I have a table like following
well,here in this table every user has a parent user,then if we select a user then its id ,children ids and children childrens ids should return as array.I need a query to get this values in rails with out using any gem.Thanx for your help:->

Answer 1

class User << ActiveRecord::Base
def self.build_tree(reverse=false)
g = Array.new
self.find(:all).each do |p|
if reverse
g << [p.id,p.parent]
else
g << [p.parent,p.id]
end
end
g
end
def self.subordinates(man_id)
g = self.build_tree false
g.map{|i| i[1] if i[0]==man_id.to_i}.compact
end
def self.superiors(user_id)
g = self.build_tree true
g.map{|i| i[1] if i[0]==user_id.to_i}.compact
end
end
When call either Superiors(parents) or Subordinates(childrends) it will gives required result
Ex:- [2,4,6,8]
If you want to get either children->childrends or parent->parents just do iterate call function either superior or subordinates until get the nil or [] array .

Answer 2

You are stranding into SQL anti-pattern. Performing operations on trees constructed like that is very inefficient. I don't say, that you should use a gem for that, but consider using some smarter method of keeping this data (searching for sql tree structure should yield some meaningful results).
Query you are looking for needs two self joins:
SELECT t1.id user_ids, t2.id children_ids, t3.id children_children_ids FROM users t1
LEFT JOIN users t2 ON t2.parent = t1.id
LEFT JOIN users t3 ON t3.parent = t2.id
On the other hand, if your rails models have defined self-relation, you could easily write:
user.children #=> (array of children)
user.children.flat_map(&:children) #=> (array of grandchildren)
Definition of this relation should look like:
class User << ActiveRecord::Base
has_many :children, class_name: User, foreign_key: 'parent'
end