CODEWITHSUNDEEP
arraysjsongounmarshalling
Kurse
Kurse

Reputation: 33

Golang Unmarshall specific object in nested JSON

what is the best practice to unmarshall a specific part of a large JSON with static property names in GO?

my JSON map looks like

{
    "top_view" : {
       "@self" : "https://generic.com",
           "graph" : {
              "nodes" : [ { } ],
              "relations" : [ { } ]
                     },
         "view_status" : {}
                 }
}

and I only need to retrieve the Nodes array

Here is what I got so far,

https://play.golang.org/p/btfRojEGqUu

I only know how to unmarshall the Nodes part, but I don't know how to tell Go to start unmarshalling only that object, so the code won't work if I feed the entire JSON tree. Please advise, thanks!

Upvotes: 1

Views: 1479

Answers (2)

Prasanth
Prasanth

Reputation: 43

This is one way to do it: Define a struct that shows the path to the Node. You can skip the members in the JSON that are not interesting. For example:

type Whole struct {
    TopView struct {
        Self  string `json:"@self"`
        Graph struct {
            Nodes []Node `json:"nodes"`
        } `json:"graph"`
    } `json:"top_view"`
}

Then marshal out the Node

var whole Whole

err := json.Unmarshal([]byte(jsonResp), &whole)

Here is the working code : https://play.golang.org/p/5WvPocce_vh

Upvotes: 1

Abhay Kumar
Abhay Kumar

Reputation: 550

You can unmarshall any JSON data without any concrete type defined in the go code. An use type assertion and type switch to drill-down the data just unmarshlled.

Below is working example of your problem using above mentioned concepts. You may need to further refine this basis your requirement, but basic concept remains the same:

package main

import (
    "encoding/json"
    "fmt"
    "log"
)

func main() {
    jsonResponse := `{
        "top_view" : {
           "@self" : "https://generic.com",
               "graph" : {
                  "nodes" : [ {
                    "@self" : "https://generic.com:443",
                    "id" : "1;;45d554600be28ee49c99d26e536225ea;;461ff354437881f6b5973d4af366b91c;;4c0f2cc8e29a4fe09240b2a0c311508d",
                    "ci" : {
                       "id" : "4c0f2cc8e29a4fe09240b2a0c311508d",
                       "name" : "NOICE",
                       "type" : "ci_collection",
                       "type_label" : "CiCollection",
                       "icon" : "/logical_group_32.svg"
                    },
                    "has_children" : true
                 }, {
                    "@self" : "https://generic.com:443hjkhk",
                    "id" : "1;;45d554600be28ee49c99d26e536225ea;;4e22910a478bf6939aed36fef22dc79e;;4a7788eeecbbeee3a8bb3189ba67f269",
                    "ci" : {
                       "id" : "4a7788eeecbbeee3a8bb3189ba67f269",
                       "name" : "NOTNOICE",
                       "type" : "ci_collection",
                       "type_label" : "CiCollection",
                       "icon" : "/logical_group_32.svg"
                    },
                    "has_children" : true
                 }, {
                    "@self" : "https://generic.com:443/fghfgh",
                    "id" : "1;;45d554600be28ee49c99d26e536225ea;;461ff354437881f6b5973d4af366b91c;;4c0f2cc8e29a4fe09240b2a0c311508d;;40b8b314821d01ac874f7209c228ab8f",
                    "ci" : {
                       "id" : "40b8b314821d01ac874f7209c228ab8f",
                       "name" : "NOICE",
                       "type" : "ci_collection",
                       "type_label" : "CiCollection",
                       "icon" : "/logical_group_32.svg"
                    },
                    "has_children" : true
                 }, {
                    "@self" : "https://generic.com:443/gfhgh",
                    "id" : "1;;45d554600be28ee49c99d26e536225ea;;4a208e0deee006668bb3cfab6541a869;;4bd30d48bc1c81b398e17435ba519f2d;;4a1c671cefd3b5b9931b4312382ff2e4",
                    "ci" : {
                       "id" : "4a1c671cefd3b5b9931b4312382ff2e4",
                       "name" : "AAA",
                       "type" : "ci_collection",
                       "type_label" : "CiCollection",
                       "icon" : "/logical_group_32.svg"
                    },
                    "has_children" : true
                 } ],
                  "relations" : [ { } ]
                         },
             "view_status" : {}
                     }
    }`

    var res interface{}
    err := json.Unmarshal([]byte(jsonResponse), &res)
    if err != nil {
        log.Fatal(err)
    }

    parseArbitoryJSONObject(res)
}

func parseArbitoryJSONObject(jsonObject interface{}) {
    data := jsonObject.(map[string]interface{})

    for k, v := range data {
        switch val := v.(type) {
        case string:
            fmt.Println(k, "is string:", val)
        case float64:
            fmt.Println(k, "is float64", val)
        case bool:
            fmt.Println(k, "is boolean", val)
        case []interface{}:
            fmt.Println(k, "is an array:")
            for i, u := range val {
                fmt.Println(i, u)
            }
        case map[string]interface{}:
            fmt.Println(k, "is an map[string]interface{}:")
            parseArbitoryJSONObject(val)
        default:
            fmt.Println(k, "is of a type I don't know how to handle")
        }
    }
}

Here the json.Unmarshal is using empty interface which can hold any value. And function parseArbitoryJSONObject() is using type assertion to facilitate value extraction from the unmarshlled data.

The type switch is where you may need to further put or modify logic to get the desired item from the unmarshlled JSON object.

below is the go-playground code snippet link for your reference:

https://play.golang.org/p/VUJsSXxSfVG

Upvotes: -1

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