Converting JSON with array

Question

I have written following code to get array from JSON, and want to retrieve something like

[{"id":"id1","friendly":"friendly1"},{"id":"id2","friendly":"friendly2"}]

But it's empty:

[{"id":"","friendly":""},{"id":"","friendly":""}]

package main

import (
    "encoding/json"
    "fmt"
)

var input = `[
            {
                "not needed": "",
                "_source": {
                    "id": "id1",
                    "friendly": "friendly1"
                }
            },
            {
                "_source": {
                    "id": "id2",
                    "friendly": "friendly2"
                }
            }]`

type source struct {
    Id string `json:"id"`
    Friendly string `json:"friendly"`
}

func main() {
    result := make([]source, 0)
    sources := []source{}

    json.Unmarshal([]byte(input), &sources)

    for _, n := range sources {
        result = append(result, n)
    }
    out, _ := json.Marshal(result)
    fmt.Println(string(out))
}

Your JSON isn't an array of sources. It's an array of objects, each of which has a field _source, which is a source. You have nothing that maps to that outer wrapper object. — Adrian
– Adrian, Commented Mar 12, 2020 at 18:50
Either play.golang.com/p/PuyliXTp_E5 or play.golang.com/p/SqWDcodPUwU (in the 2nd one you can omit the loop for the marshaling play.golang.com/p/o1vOUgTPjmh) — mkopriva
– mkopriva, Commented Mar 12, 2020 at 19:21

Rodrigo Carvalho · Accepted Answer · 2020-03-12 20:25:05Z

Try creating an another struct that have one field called Source of type source. In my example below I called this struct outer. Your input should be an array of outer and your result an array of source.

Something like this:


import (
    "encoding/json"
    "fmt"
)

var input = `[
            {
                "not needed": "",
                "_source": {
                    "id": "id1",
                    "friendly": "friendly1"
                }
            },
            {
                "_source": {
                    "id": "id2",
                    "friendly": "friendly2"
                }
            }]`

type outer struct {
    Source source `json:"_source"`
}

type source struct {
    Id string `json:"id"`
    Friendly string `json:"friendly"`
}

func main() {
    result := make([]source, 0)
    sources := []outer{}

    json.Unmarshal([]byte(input), &sources)

    for _, n := range sources {
        result = append(result, n.Source)
    }
    out, _ := json.Marshal(result)
    fmt.Println(string(out))
}```

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