Unmarshal partial data bytes into a custom structure

Question content

I have data in the form of map[string][]byte, where key is the json field tag of the structure, value is a slice of bytes.

Consider this example:

type Tweet struct {
    UserId int `json:"user_id"`
    Message string `json:"message"`
}

data = {
"user_id":<some bytes>,
"message":<some bytes>
}

var t Tweet

How to unmarshal the corresponding field data into a Tweet structure, which can contain any type of field, i.e. slice/map/custom type/pointer type? Do I have to map each field's data individually one by one or is there any general way?

I tried marshalling the entire data and unmarshalling it back into a struct type, but it seems like it internally modifies the actual data and doesn't work.

bytes, err := json.Marshal(data)
var t Tweet
err = json.Unmarshal(bytes,&t)

Workaround

I don't think you mentioned your error, but the following worked for me. You can try this.

package main

import (
    "encoding/json"
    "fmt"
)

type Tweet struct {
    UserId  int    `json:"user_id"`
    Message string `json:"message"`
}

func main() {
    // Example data: map of field tags to JSON-encoded byte slices
    data := map[string]json.RawMessage{
        "user_id": []byte(`123`),             // Encoded as a JSON number
        "message": []byte(`"Hello, world!"`), // Encoded as a JSON string
    }

    // Convert map to JSON
    jsonData, err := json.Marshal(data)
    if err != nil {
        fmt.Println("Error marshalling map to JSON:", err)
        return
    }

    // Unmarshal JSON into Tweet struct
    var t Tweet
    if err := json.Unmarshal(jsonData, &t); err != nil {
        fmt.Println("Error unmarshalling JSON:", err)
        return
    }

    // Output the result
    fmt.Printf("Unmarshalled: %+v\n", t)

    // Marshal the Tweet struct back into JSON
    marshalledData, err := json.Marshal(t)
    if err != nil {
        fmt.Println("Error marshalling Tweet struct to JSON:", err)
        return
    }

    // Output the marshalled JSON
    fmt.Printf("Marshalled: %s\n", marshalledData)
}

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