Convert struct to json array instead of json object

Question

I apologise in advance if this question is considered too easy or whatever; this is the first time I'm writing anything in go. I have two structs (simplified for this question)

type A struct {
    Content string
}

type B struct {
    Element A `json:"0"`
    Children []B `json:"1"`
}

I want to encode a value of type B into JSON, but instead of returning an object it should return a json array

For example:

What I get:

[
    {
        "0":{
            "Content":"AAA"
        },
        "1":[
            {
                "0":{
                    "Content":"BBB"
                },
                "1":[
                    {
                        "0":{
                            "Content":"CCC"
                        },
                        "1":[]
                    },
                    {
                        "0":{
                            "Content":"DDD"
                        },
                        "1":[]
                    }
                }
            ]
        ]
    }
]

What I need:

[
    {"Content": "AAA"}, 
    [
        [
            {"Content": "BBB"},
            [
                {"Content": "CCC"}, 
                []
            ]
        ], 
        [
            {"Content": "DDD"}, 
            []
        ]
    ]
]

I could do this by manually iterating through it, but I would hope that there's an integrated way to do it

Please format your JSON strings usign line breaks & indent. It's not readable at the moment and hard to understand the difference. — Alexander Trakhimenok
– Alexander Trakhimenok, Commented Nov 1, 2017 at 16:12
There isn't. A Go struct equates to a JSON object, not a JSON array. You could do it yourself with a custom UnmarshalJSON. — Adrian
– Adrian, Commented Nov 1, 2017 at 16:13

Koala Yeung · Accepted Answer · 2017-11-02 05:50:29Z

You may do so by implementing json.Marshaler interface in B.

For example: https://play.golang.org/p/fT1WlQ5Raz

package main

import (
    "encoding/json"
    "fmt"
)

type A struct {
    Content string
}

type B struct {
    Element  A
    Children []B
}

// MarshalJSON implements json.Marshaler
func (b B) MarshalJSON() ([]byte, error) {
    return json.Marshal([]interface{}{
        b.Element,
        b.Children,
    })
}

func main() {

    root := B{
        Element: A{Content: "AAA"},
        Children: []B{
            B{
                Element: A{Content: "BBB"},
                Children: []B{
                    B{Element: A{Content: "CCC"}, Children: []B{}},
                    B{Element: A{Content: "DDD"}, Children: []B{}},
                },
            },
        },
    }

    content, _ := json.MarshalIndent(root, "", "  ")
    fmt.Printf("%s\n", content)
}

Results:

[
  {
    "Content": "AAA"
  },
  [
    [
      {
        "Content": "BBB"
      },
      [
        [
          {
            "Content": "CCC"
          },
          []
        ],
        [
          {
            "Content": "DDD"
          },
          []
        ]
      ]
    ]
  ]
]

Kebeng · Accepted Answer · 2017-11-01 17:49:42Z

0

i think you need a slice of interface to wrap both A and B struct into a single slice

please take a look at my snippet here https://play.golang.org/p/c0xldskKyz

answered Nov 1, 2017 at 17:49

Kebeng

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