How to parse json array struct

Question

I'm using the following code without success to parse json value but its inside array []

https://play.golang.org/p/5HdWeyEtvie

package main

import (
    "encoding/json"
    "fmt"
)


var input = `
[
{
    "created_at": "Thu May 31 00:00:01 +0000 2012"
},
{
    "created_at": "Thu May 31 00:00:01 +0000 2012"
}
]
`

func main() {
    var val map[string]interface{}
    if err := json.Unmarshal([]byte(input), &val); err != nil {
        panic(err)
    }
    fmt.Println(val)
}

The idea is to get the value as key and print it , like a function that get string parameter="created_at" and prints it.

Answer 1

You're unmarshaling an array to a map. That obviously won't work. you need val to be an array.

func main() {
    var val []map[string]interface{} // <---- This must be an array to match input
    if err := json.Unmarshal([]byte(input), &val); err != nil {
        panic(err)
    }
    fmt.Println(val)
}

Answer 2

Your input is:

[  
   {  
      "created_at":"Thu May 31 00:00:01 +0000 2012"
   },
   {  
      "created_at":"Thu May 31 00:00:01 +0000 2012"
   }
]

You can turn this into a struct like so:

type MyArray []struct {
    CreatedAt string `json:"created_at"`
}

Now you can read your JSON data and loop through it to get your desired values. Here's what you get:

package main

import (
    "encoding/json"
    "fmt"
)

var str = `[
    {
    "created_at": "Thu May 31 00:00:01 +0000 2012"
    },
    {
    "created_at": "Thu May 31 00:00:01 +0000 2013"
    }
]`

type MyArray struct {
    CreatedAt string `json:"created_at"`
}

func main() {
    var m []MyArray
    if err := json.Unmarshal([]byte(str), &m); err != nil {
        panic(err)
    }
    for _, val := range m {
        fmt.Println(val.CreatedAt)
    }
}

In the future, you could consult JSON-to-Go if you're unsure how to convert a JSON object to a struct -- it's quite useful. Cheers!

Answer 3

You should create a struct like this.

type Data struct {
    CreateAt time.Time `json:"create_at"`
}

func main() {
    var in []Data
    if err := json.Unmarshal([]byte(input), &in); err != nil{
        log.Fatal(err)
    }
    for _, data := range in{
        fmt.Println(data.CreateAt)
    }
}

Answer 4

var input = `[
    {
    "created_at": "Thu May 31 00:00:01 +0000 2012"
    },
    {
    "created_at": "Thu May 31 00:00:01 +0000 2013"
    }
]`

func main() {
    var val []struct {
        CreatedAt string `json:"created_at"`
    }

    if err := json.Unmarshal([]byte(input), &val); err != nil {
        panic(err)
    }

    fmt.Println(val[0].CreatedAt)
}