Decoding a slice of maps from a JSON string in Golang

Question

Following the Go by Example: JSON tutorial, I see how to work with a basic JSON string:

package main

import (
    "encoding/json"
    "fmt"
    )

type Response struct {
    Page   int      `json:"page"`
    Fruits []string `json:"fruits"`
}

func main() {
    str := `{"page": 1, "fruits": ["apple", "peach"]}`
    res := Response{}
    json.Unmarshal([]byte(str), &res)
    fmt.Println(res.Page)
    fmt.Println(res.Fruits)
}

// the output looks good here:
// 1
// [apple peach]

I would like to add some complexity to the str data object that I am decoding.

Namely, I would like to add a key with a slice of maps as its value:

"activities": [{"name": "running"}, {"name", "swimming"}]

My script now looks like below example, however, for the life of me, I can not figure out what the correct syntax is in the Response struct in order to get at the values in activities. I know that this syntax isn't correct: Activities []string ... but can not hack my way towards a solution that captures the data I want to display.

package main

import (
    "encoding/json"
    "fmt"
    )

type Response struct {
    Page   int      `json:"page"`
    Fruits []string `json:"fruits"`
    Activities []string `json:"activities"`
}

func main() {
    str := `{"page": 1, "fruits": ["apple", "peach"], "activities": [{"name": "running"}, {"name", "swimming"}]}`
    res := Response{}
    json.Unmarshal([]byte(str), &res)
    fmt.Println(res.Page)
    fmt.Println(res.Fruits)
    fmt.Println(res.Activities)
}

// the script basically craps out here and returns:
// 0
// []
// []

Thanks for any help!

user5728991 · Accepted Answer · 2016-02-23 02:36:09Z

4

Use []map[string]string:

type Response struct {
    Page   int      `json:"page"`
    Fruits []string `json:"fruits"`
    Activities []map[string]string `json:"activities"`
}

playground example

Always check and handle errors. The example JSON has a syntax error which is corrected in the playground example.

answered Feb 23, 2016 at 2:36

user5728991

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Comments

Maciek.Z · Accepted Answer · 2017-06-17 23:02:51Z

0

I know this is an old one, but i've recently written utility for generating exact go type from json input and in similar case you could give it a spin: https://github.com/m-zajac/json2go

For this particular example it generates from json:

{"page": 1, "fruits": ["apple", "peach"], "activities": [{"name": "running"}, {"name": "swimming"}]}

go type:

type Object struct {
    Activities  []struct {
        Name string `json:"name"`
    }   `json:"activities"`
    Fruits  []string    `json:"fruits"`
    Page    int     `json:"page"`
}

answered Jun 17, 2017 at 23:02

Maciek.Z

1

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