How Can I Partially Unmarshal JSON into a Go Map?

Partially JSON Unmarshal into a Map in Go

In Go, it's possible to partially unmarshal JSON data into a map when the data is wrapped in an object with key-value pairs. This allows for easy identification of the type of value each key holds.

Implementation

To achieve this, use the encoding/json package and unmarshal into a map[string]json.RawMessage. The json.RawMessage type captures the underlying JSON data before further parsing.

var objmap map[string]json.RawMessage
err := json.Unmarshal(data, &objmap)

Further Parsing

Once the map is obtained, you can proceed to parse the value of each key according to its known type.

For the example JSON:

{
    "sendMsg":{"user":"ANisus","msg":"Trying to send a message"},
    "say":"Hello"
}

You can parse sendMsg and say as follows:

type sendMsg struct {
    User string
    Msg  string
}

var s sendMsg
err = json.Unmarshal(objmap["sendMsg"], &s)

var str string
err = json.Unmarshal(objmap["say"], &str)

Exporting Variables

Note that the variables in the sendMsg struct must be exported (i.e., capitalized) for proper unmarshaling, as shown:

type sendMsg struct {
    User string
    Msg  string
}

Example

See a working example here: https://play.golang.org/p/OrIjvqIsi4-

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