Getting to a specific key in JSON array using Go

Question

I've had a heck of a time parsing JSON strings and finally landed on https://github.com/bitly/go-simplejson. It looks really promising but it's still giving me an empty result for the following JSON array:

{
 "data": {
  "translations": [
   {
    "translatedText": "Googlebot: Deutsch, um die Luft-Speed-Geschwindigkeit einer unbeladenen Schwalbe?"
   }
  ]
 }
}

I want to get to translatedText by only specifying the key. The reason for this is my JSON structure won't be predictable and so I'd like to target any JSON array but specifying a key without knowing the full structure of the JSON array.

This is the snippet of code I use where content contains the JSON byte array:

f, err := js.NewJson(content)

if err != nil {
    log.Println(err)
}

t := f.Get("translatedText").MustString()

log.Println(t)

t is always blank :( Would appreciate any pointers.

ANisus · Accepted Answer · 2014-03-27 01:46:29Z

The problem you have is that the function Get does not recursively search through the structure; it only does a look up for the key the at the current level.

What you can do is to create a recursive function that searches the structure and returns the value once it is found. Below is a working example using the standard package encoding/json:

package main

import (
    "encoding/json"
    "fmt"
)

// SearchNested searches a nested structure consisting of map[string]interface{}
// and []interface{} looking for a map with a specific key name.
// If found SearchNested returns the value associated with that key, true
// If the key is not found SearchNested returns nil, false
func SearchNested(obj interface{}, key string) (interface{}, bool) {
    switch t := obj.(type) {
    case map[string]interface{}:
        if v, ok := t[key]; ok {
            return v, ok
        }
        for _, v := range t {
            if result, ok := SearchNested(v, key); ok {
                return result, ok
            }
        }
    case []interface{}:
        for _, v := range t {
            if result, ok := SearchNested(v, key); ok {
                return result, ok
            }
        }
    }

    // key not found
    return nil, false
}


func main() {
    jsonData := []byte(`{
 "data": {
  "translations": [
   {
    "translatedText": "Googlebot: Deutsch, um die Luft-Speed-Geschwindigkeit einer unbeladenen Schwalbe?"
   }
  ]
 }
}`)

    // First we unmarshal into a generic interface{}
    var j interface{}
    err := json.Unmarshal(jsonData, &j)
    if err != nil {
        panic(err)
    }

    if v, ok := SearchNested(j, "translatedText"); ok {
        fmt.Printf("%+v\n", v)
    } else {
        fmt.Println("Key not found")
    }

}

Result:

Googlebot: Deutsch, um die Luft-Speed-Geschwindigkeit einer unbeladenen Schwalbe?

Playground: http://play.golang.org/p/OkLQbbId0t

@Etienne: Welcome! Just be aware that, if you have multiple instances of the same key name in the structure, it will return the first it finds. And if you use nested JSON objects and not just arrays (which you seem to do), it will be arbitrary which value is returned. Happy Go coding!

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