mapping-json.go

package main

import (
	"encoding/json"
	"fmt"
	"github.com/fatih/structs"
	"reflect"
	"strings"
)

type Nested struct{
	Names []string
}

type JsonData struct {
	RID string `json:"r_id,omitempty"`
	Title string `json:"title,omitempty"`
	Address struct {
		City struct {
			ID string `json:"id,omitempty"`
			Name string `json:"name,omitempty"`
		} `json:"city,omitempty"`
		Postal string `json:"postal,omitempty"`
	} `json:"address"`
	Description string `json:"description,omitempty"`
}

func main() {

	file := []byte(`{
			  "r_id" : "123456",
			  "title" : "brand new restarant with changed name",
			  "address": {
			      "city": {
				"id": "25",
				"name": "Dhaka"
			      },
			      "postal":"1213"
			  },
			  "description" : "here are some new desciption "
			}`)

	var res JsonData

	err := json.Unmarshal(file, &res)
	if err != nil {
		fmt.Printf("err : %s", err.Error())
	}

	field := structs.Fields(res)

	patch := make(map[string]interface{})

	result := mapFields(field, patch, &Nested{})

	fmt.Printf("%v", result)
	
	// prints :  map[address.city.id:25 address.city.name:Modhubag r_id:123456 title:brand new restarant with changed name]
	// But not all string field like description and state of address

}

func mapFields(field []*structs.Field, patch map[string]interface{}, names *Nested) map[string]interface{} {

	for _, k := range field {
		if !k.IsZero() {
			rf := reflect.TypeOf(k.Value())
			switch rf.Kind() {
			case reflect.String:
				fname := strings.Split(k.Tag("json"), ",") // to remove omitempty and get only the json field name
				if len(names.Names) > 0 {
					join := strings.Join(names.Names, ".")
					patch[join+"."+fname[0]] = k.Value()
				}else {
					patch[fname[0]] = k.Value()
				}
			case reflect.Ptr:
				fname := strings.Split(k.Tag("json"), ",")
				names.Names = append(names.Names, fname[0])
				return mapFields(k.Fields(), patch, names)
			}
		}
	}

	return patch
}