main.go

package main

import (
	"fmt"
)

/**
 * DB structure if we use Mysql
 DROP TABLE IF EXISTS `employees`;
 CREATE TABLE `employees` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `manager_id` int(10) unsigned DEFAULT NULL,
  `name` varchar(512) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `created_at` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
  `updated_at` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
*/

/**
 * Recursive sql if we using Mysql 8 +
 * This will avoid printing out any unrelated employee
WITH RECURSIVE EmployeeStuct AS (
    SELECT * FROM employees WHERE manager_id IS NULL
    UNION ALL
    SELECT m.* FROM employees AS m JOIN EmployeeStuct AS t ON m.manager_id = t.id
)
SELECT * FROM EmployeeStuct;
*/

type Employee struct {
	Id        int
	ManagerId int
	Name      string
}
type EmployeeTree struct {
	Id        int
	ManagerId int
	Name      string
	son       []EmployeeTree
}

var allEmployees = []Employee{
	Employee{100, 150, "Alan"},
	Employee{220, 100, "Martin"},
	Employee{150, 0, "Jamie"},
	Employee{275, 100, "Alex"},
	Employee{400, 150, "Steve"},
	Employee{190, 400, "David"},
}

func main() {
	arr := recursiveTree(allEmployees, 0)
	fmt.Println(arr)

}

// function to group the employees accordingly to their manager
func recursiveTree(allEmployee []Employee, ManagerId int) []EmployeeTree {
	var arr []EmployeeTree
	for _, v := range allEmployee {
		if ManagerId == v.ManagerId {
			ctree := EmployeeTree{}
			ctree.Id = v.Id
			ctree.ManagerId = v.ManagerId
			ctree.Name = v.Name

			sonE := recursiveTree(allEmployee, v.Id)
			ctree.son = sonE
			arr = append(arr, ctree)
		}
	}
	return arr
}