RoR, need to create recursive relationships in table associations - mysql

Question

I'm very new to rails, and am a little stuck on the logic for this problem.
I have one table (using mysql) of employees, each of them with a manager_id key which refers to the employee they report to. So for example the employee with the title of "CEO" with an id of 1, has a manager_id of nil, and the employee with title of "CTO" has a manager_id of 1. So my records look like this
id: 1, first_name: "Bob", last_name: "Boss", title: "CEO", manager_id: null
id: 2, first_name: "Pat", last_name: "Guy", title: "CTO", manager_id: 1
id: 3, first_name: "John", last_name: "Dude", title: "VP of engineering", manager_id: 2
and my JSON structure should look like this
[
{id: 1, first_name: "Bob", last_name: "Boss", title: "CEO", manager_id: null, descendents: [
{id: 2, first_name: "Pat", last_name: "Guy", title: "CTO", manager_id: 1, descendents: [
{id: 3, first_name: "John", last_name: "Dude", title: "VP of engineering", manager_id: 2, descendents: [....]}
]},
{..more CEO descendents...}
]
I'm trying to create a nested JSON structure that starts at CEO, lists all employees that report to them, and each of those employees descendants. I was trying to write a script that creates this but I keep getting infinite recursive calls. This is what I have
#start at some root
#root = Employee.find_by title: 'CEO'
#convert to hash table
#results[0] = #root.attributes
#add direct_reports key
#results[0]["direct_reports"] = []
def getBelow(root=#root)
#reports = Employee.where("manager_id = ?", #root[:id])
if #reports.blank?
return []
else
#reports = #reports.map(&:attributes)
#reports.each do |person|
person["direct_reports"] = []
getBelow(person)
end
#reports = Employee.where("manager_id = ?", #root[:id])
root["direct_reports"] = #reports
end
return #root
end
#list = getBelow(#results[0])
If I'm passing in each new person object, shouldn't they all eventually end when #reports.blank? becomes true?
An alternative I was thinking of was to use table associations inspired by this blog post
https://hashrocket.com/blog/posts/recursive-sql-in-activerecord
but that seems a little too complicated.

Answer 1

Some issues in the getBelow method
You are always using #root, instead of using the param (root). So you are always starting again from the 'CEO'.
You are calling getBelow recursively but you are not using the result.
You call #reports = Employee.where("manager_id = ?", #root[:id]) twice.
You return #root.
As Jorge Najera said, there are gems that handle a tree structure easily. If you want to build it on your own, this is my suggestion:
#start at some root
#root = Employee.find_by manager_id: nil
#convert to hash table
#tree = #root.attributes
#add direct_reports key
#tree["direct_reports"] = getBelow(#root)
def getBelow(manager)
branch = []
Employee.where("manager_id = ?", manager.id).each do |employee|
node = employee.attributes
node["direct_reports"] = getBelow(employee)
branch << node
end
branch
end
This was not tested so I think you´ll get some errors, but I believe the idea is fine.