golang why is value overwritten while implementing hierarchy tree? - go

Question

package main
import (
"encoding/json"
"fmt"
)
type employee struct {
Name string `json:"name"`
Id int `json:"id,omitempty"`
ManagerId int `json:"managerid"`
Reporters []employee `json:"reporters,omitempty"`
}
// type employees struct {
// employees []employee `json:"employee"`
// }
type EmployeeList struct {
employees map[int]employee
root employee
}
func NewEmployeeList() *EmployeeList {
var el EmployeeList
el.employees = make(map[int]employee)
return &el
}
func (el *EmployeeList) CreateMap(employeesInfo []employee) {
for _ , emp := range employeesInfo {
e := employee{
Name : emp.Name,
Id: emp.Id,
ManagerId: emp.ManagerId,
}
el.employees[emp.Id] = e
if(emp.ManagerId == 0){
el.root = e
fmt.Println("CreateMap",el.root)
}
}
fmt.Println("CreateMap2",el.root,el.employees)
}
func (el *EmployeeList) getReportersById(empId int) []employee {
reporters := []employee{}
for _ , employee := range el.employees {
if(employee.ManagerId == empId){
reporters = append(reporters, employee)
}
}
return reporters
}
func (el *EmployeeList) maketree(e *employee) {
//e := root
e.Reporters = el.getReportersById(e.Id)
if(true){
fmt.Println("maketree",e.Id,e.Name,e.Reporters)
}
// e.Reporters = reporters
if(len(e.Reporters) == 0){
return
}
for _ , reporterEmployee := range e.Reporters {
el.maketree(&reporterEmployee);
}
}
func (el EmployeeList) print(root employee, level int) {
for i:= 0; i<level;i++ {
fmt.Print("\t");
}
fmt.Println(root.Name);
for _, reporter := range root.Reporters {
el.print(reporter, level + 1)
}
}
func main() {
//1. Read JSON File
myJsonString := `[{ "name": "Rob", "id": 7, "managerid": 3 }, { "name": "Rex", "id": 6, "managerid": 2 }, { "name": "Jake", "id": 5, "managerid": 2 }, { "name": "Paul", "id": 4, "managerid": 1 }, { "name": "Oliver", "id": 3, "managerid": 1 }, { "name": "John", "id": 2, "managerid": 1 }, { "name": "Britney", "id": 1, "managerid": 0 }]`
//2. Create class and sent file data
emplist := NewEmployeeList()
rawEmployeesInfo := []employee{}
_ = json.Unmarshal([]byte(myJsonString),&rawEmployeesInfo);
//fmt.Println(rawEmployeesInfo);
emplist.CreateMap(rawEmployeesInfo);
//fmt.Println(emplist.employees,emplist.root);
fmt.Println("Main1",emplist.root)
emplist.maketree(&emplist.root);
//fmt.Println(emplist.root)
fmt.Println("Main2",emplist.root)
emplist.print(emplist.root,0)
}
I am trying to create a tree from a json to store employee list. The problem is that while creating the tree values are stored correctly but somehow they lose value in the main function when I want to print the hierarchy tree. Can someone please help me why the value is not stored? I have added logs also to check.

Answer 1

Your CreateMap method:
func (el EmployeeList) CreateMap(employeesInfo []employee) {
...
}
should be:
func (el *EmployeeList) CreateMap(employeesInfo []employee) {
//---^
....
}
so that el is a pointer. Otherwise you're operating on a copy of emplist when you say:
emplist.CreateMap(rawEmployeesInfo);
so you do a bunch of work to create your map and then throw it all away.