Golang Converting JSON

Question

map[key:2073933158088]

I need to grab the key out of this data structure as a string, but I can't seem to figure out how!

Help with this overly simple question very much appreciated.

The value above is encapsulated in the variable named data.

I have tried: data.key, data[key], data["key"], data[0] and none of these seem to be appropriate calls.

To define data I sent up a JSON packet to a queue on IronMQ. I then pulled the message from the queue and manipulated it like this:

payloadIndex := 0

for index, arg := range(os.Args) {
        if arg == "-payload" {
                payloadIndex = index + 1
        }
}

if payloadIndex >= len(os.Args) {
        panic("No payload value.")
}

payload := os.Args[payloadIndex]

var data interface{}

raw, err := ioutil.ReadFile(payload)

if err != nil {
    panic(err.Error())
}

err = json.Unmarshal(raw, &data)

Have you attempted anything? It'd be good to show at least some sample code or attempts that you've made. — Leo Correa
– Leo Correa, Commented Apr 7, 2014 at 18:08
Edited it to give more context. The calls I get give me errors saying "invalid operation" or "type interface {} has no field or method key" — Jorge Olivero
– Jorge Olivero, Commented Apr 7, 2014 at 18:11
@JorgeOlivero, that isn't valid JSON, and decoding into an interface{} makes no sense. You need to declare some sort of data structure to contain what you're decoding. You could even use a map[string]string if you want. — Mr_Pink
– Mr_Pink, Commented Apr 7, 2014 at 18:31

Grzegorz Żur · Accepted Answer · 2014-04-07 18:32:51Z

2

Design your data type to match json structure. This is how can you achieve this:

package main

import (
    "fmt"
    "encoding/json"
)

type Data struct {
    Key string `json:"key"`
}

func main() {
    data := new(Data)
    text := `{ "key": "2073933158088" }`
    raw := []byte(text)
    err := json.Unmarshal(raw, data)
    if err != nil {
        panic(err.Error())  
    }
    fmt.Println(data.Key)
}

answered Apr 7, 2014 at 18:32

Grzegorz Żur

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Comments

fsouza · Accepted Answer · 2014-04-07 18:53:41Z

Since the number in the json is unquoted, it's not a string, Go will panic if you try to just handle it as a string (playground: http://play.golang.org/p/i-NUwchJc1).

Here's a working alternative:

package main

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

type Data struct {
    Key string `json:"key"`
}

func (d *Data) UnmarshalJSON(content []byte) error {
    var m map[string]interface{}
    err := json.Unmarshal(content, &m)
    if err != nil {
        return err
    }
    d.Key = strconv.FormatFloat(m["key"].(float64), 'f', -1, 64)
    return nil
}

func main() {
    data := new(Data)
    text := `{"key":2073933158088}`
    raw := []byte(text)
    err := json.Unmarshal(raw, data)
    if err != nil {
        panic(err.Error())
    }
    fmt.Println(data.Key)
}

You can see the result in the playground: http://play.golang.org/p/5hU3hdV3kK

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