How to unmarshal dynamic json objects with Golang

Question

let me start by telling that I'm pretty recent in the Go world.

What I'm trying to do is to read the json I get from a JSON API (I don't control). Everything is working fine, I can show the received ID and Tags too. But the fields field is a little bit different, because its a dynamic array.

I can receive from the api this:

{
    "id":"M7DHM98AD2-32E3223F",
    "tags": [
        {
            "id":"9M23X2Z0",
            "name":"History"
        },
        {
            "id":"123123123",
            "name":"Theory"
        }
    ],
    "fields": {
        "title":"Title of the item",
        "description":"Description of the item"
    }
}

Or instead of title and description I could receive only description, or receive another random object like long_title. The objects return may differ completly and can be an infinite possibility of objects. But it always returns objects with a key and a string content like in the example.

This is my code so far:

type Item struct {
    ID string `json:"id"`
    Tags []Tag `json:"tags"`
    //Fields []Field `json:"fields"`
}

// Tag data from the call
type Tag struct {
    ID string `json:"id"`
    Name string `json:"name"`
}

// AllEntries gets all entries from the session
func AllEntries() {
    resp, _ := client.Get(APIURL)
    body, _ := ioutil.ReadAll(resp.Body)

    item := new(Item)
    _ = json.Unmarshal(body, &item)

    fmt.Println(i, "->", item.ID)
}

So the Item.Fields is dynamic, there is no way to predict what will be the key names, and therefore as far I can tell, there is no way to create a struct for it. But again, I'm pretty newbie with Go, could someone give me any tips? Thanks

What are you going to do with that data if you don't know what to expect them to be ? What do you needfields for ? — hlscalon
– hlscalon, Commented Dec 28, 2016 at 18:43

Ashwini Chaudhary · Accepted Answer · 2017-01-02 23:07:39Z

8

If the data in "fields" is always going to be a flat-dict then you can use map[string]string as type for the Fields.

For arbitrary data specify Fields as a RawMessage type and parse it later on based on its content. Example from docs: https://play.golang.org/p/IR1_O87SHv

If the fields are way too unpredictable then you can keep this field as is([]byte) or if there are fields that are always going to common then you can parse those and leave the rest(but this would result in loss of data present in other fields).

edited Jan 2, 2017 at 23:07

answered Dec 28, 2016 at 18:46

Ashwini Chaudhary

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