How to create Category Tree in GoLang - go

Question

I have a struct like that.
type Category struct {
ID int `json:"id"`
MetaDescription string `json:"metaDescription" gorm:"column:metadescription"`
MetaTitle string `json:"metaTitle" gorm:"column:metatitle"`
Name string `json:"name" gorm:"column:categoryname"`
Order int `json:"order" gorm:"column:categoryorder"`
ParentId int `json:"parentId" gorm:"column:parentid"`
Rank float64 `json:"rank" gorm:"column:rank"`
Url string `json:"url" gorm:"column:catname4seo"`
}
I'm fetching this data from a database and I want to manipulate it to create a category tree. My tree would be like that
type CategoryTree struct {
ID int `json:"id"`
Name string `json:"name" gorm:"column:categoryname"`
Url string `json:"url" gorm:"column:catname4seo"`
SubCategories []CategoryTree `json:"subCategories"`
}
Normally, I am a JavaScript dev and a newbie in GoLang so especially static type made me harder. That's why I couldn't achieve it. Can you help me to do so?
Thanks in advance.

Answer 1

I think this is an algorithm question. Just iterating over the Category list, and push elements into CategoryTree. Go code like this:
package main
import (
"encoding/json"
"fmt"
)
type Category struct {
ID int `json:"id"`
MetaDescription string `json:"metaDescription" gorm:"column:metadescription"`
MetaTitle string `json:"metaTitle" gorm:"column:metatitle"`
Name string `json:"name" gorm:"column:categoryname"`
Order int `json:"order" gorm:"column:categoryorder"`
ParentId int `json:"parentId" gorm:"column:parentid"`
Rank float64 `json:"rank" gorm:"column:rank"`
Url string `json:"url" gorm:"column:catname4seo"`
}
// load db data by CategoryTree instead of Category
type CategoryTree struct {
Category
SubCategories []*CategoryTree `json:"subCategories"`
}
func main() {
input := []*CategoryTree{
{
Category: Category{
ID: 1,
ParentId: 0,
},
},
{
Category: Category{
ID: 2,
ParentId: 1,
},
},
{
Category: Category{
ID: 3,
ParentId: 1,
},
},
{
Category: Category{
ID: 4,
ParentId: 2,
},
},
}
tree := makeTree(input)
output, _ := json.MarshalIndent(tree, "", " ")
fmt.Printf("%s\n", string(output))
}
func makeTree(list []*CategoryTree) *CategoryTree {
dataMap := make(map[int]*CategoryTree, len(list))
var rootNode *CategoryTree
for i := range list {
// root node has min ParentID
if rootNode == nil || rootNode.ParentId > list[i].ParentId {
rootNode = list[i]
}
// list to map
dataMap[list[i].ID] = list[i]
}
// build tree
for i := range list {
parentNode, ok := dataMap[list[i].ParentId]
if !ok {
continue
}
if parentNode.SubCategories == nil {
parentNode.SubCategories = []*CategoryTree{}
}
parentNode.SubCategories = append(parentNode.SubCategories, list[i])
}
return rootNode
}
and output:
{
"id": 1,
"metaDescription": "",
"metaTitle": "",
"name": "",
"order": 0,
"parentId": 0,
"rank": 0,
"url": "",
"subCategories": [
{
"id": 2,
"metaDescription": "",
"metaTitle": "",
"name": "",
"order": 0,
"parentId": 1,
"rank": 0,
"url": "",
"subCategories": [
{
"id": 4,
"metaDescription": "",
"metaTitle": "",
"name": "",
"order": 0,
"parentId": 2,
"rank": 0,
"url": "",
"subCategories": null
}
]
},
{
"id": 3,
"metaDescription": "",
"metaTitle": "",
"name": "",
"order": 0,
"parentId": 1,
"rank": 0,
"url": "",
"subCategories": null
}
]
}