Q:

Unmarshalling json arrays as json objects

I have to unmarshal a series of Json objects, but one of the objects contain a json array which is not really structured in a good way.
"labels": [
    {
      "key": "owner",
      "value": "harry"
    },
    {
      "key": "group",
      "value": "student"
    }
  ]

I am unmarshalling it using this struct -
type StudentDetails struct {
Id        string         `json:"id"`
Name      string         `json:"name"`
Labels    []Label   `json:"labels,omitempty"`
}
type Label struct {
Key string `json:"key"`
Value string `json:"value"`
}

And I have to access it using x.Labels[0].key == "owner" inside a for loop which is very annoying. 
I want to be able to do x.Labels.Owner == "harry" instead. How do I go about achieving this? The rest of JSON is unmarshalled fine using the default unmarshal function, so I don't think writing custom function will be good option. 

A:

With the constraints you have here, this is about as close as you will get (run in playground):
package main

import (
    "encoding/json"
    "fmt"
)

func main() {
    j := `
        {
            "id": "42",
            "name": "Marvin",
            "labels": [
                {
                    "key": "owner",
                    "value": "harry"
                },
                {
                    "key": "group",
                    "value": "student"
                }
            ]
        }`

    d := StudentDetails{}
    err := json.Unmarshal([]byte(j), &d)
    if err != nil {
        panic(err)
    }
    fmt.Println(d.Labels["owner"])
    fmt.Println(d.Labels["group"])
}

type StudentDetails struct {
    Id     string `json:"id"`
    Name   string `json:"name"`
    Labels Labels `json:"labels"`
}

type Labels map[string]string

func (l *Labels) UnmarshalJSON(b []byte) error {
    a := []map[string]string{}
    err := json.Unmarshal(b, &a)
    if err != nil {
        return err
    }

    t := map[string]string{}
    for _, m := range a {
        t[m["key"]] = m["value"]
    }
    *l = t
    return nil
}

