Golang parse JSON array into data structure

Question

I am trying to parse a file which contains JSON data:

[
  {"a" : "1"},
  {"b" : "2"},
  {"c" : "3"}
]

Since this is a JSON array with dynamic keys, I thought I could use:

type data map[string]string

However, I cannot parse the file using a map:

c, _ := ioutil.ReadFile("c")
dec := json.NewDecoder(bytes.NewReader(c))
var d data
dec.Decode(&d)


json: cannot unmarshal array into Go value of type main.data

What would be the most simple way to parse a file containing a JSON data is an array (only string to string types) into a Go struct?

EDIT: To further elaborate on the accepted answer -- it's true that my JSON is an array of maps. To make my code work, the file should contain:

{
  "a":"1",
  "b":"2",
  "c":"3"
}

Then it can be read into a map[string]string

Marko Kevac · Accepted Answer · 2014-08-23 20:25:25Z

25

Try this: http://play.golang.org/p/8nkpAbRzAD

package main

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

type mytype []map[string]string

func main() {
    var data mytype
    file, err := ioutil.ReadFile("test.json")
    if err != nil {
        log.Fatal(err)
    }
    err = json.Unmarshal(file, &data)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(data)
}

answered Aug 23, 2014 at 20:25

Marko Kevac

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1 Comment

Akavall Over a year ago

Shouldn't this type mytype []map[string]string be type mytype map[string]string ?

Steve P. · Accepted Answer · 2014-08-26 04:34:08Z

17

It's because your json is actually an array of maps, but you're trying to unmarshall into just a map. Try using the following:

type YourJson struct {
    YourSample []struct {
        data map[string]string
    } 
}

edited Aug 26, 2014 at 4:34

answered Aug 23, 2014 at 20:18

Steve P.

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3 Comments

Kiril Over a year ago

Yes, you are right! This works when the file is the same format as in my question. I edited my question to show the other possibility to make it work with a map[string]string.

Nam G VU Over a year ago

Can we have the full working code? I tried with above YourJson struct and not succeeded.

Nam G VU Over a year ago

With this type YourJson []map[string]string from stackoverflow.com/a/25466050/248616 works for me

JessonChan · Accepted Answer · 2014-08-25 07:47:46Z

4

you can try the bitly's simplejson package
https://github.com/bitly/go-simplejson

it's much easier.

answered Aug 25, 2014 at 7:47

JessonChan

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