How to add a valid json string to an object

I currently have something like this

type Info struct {
	Ids        []string `json:"ids"`
	assignment string   `json:"assignment"`
}

Now my assignment is a large hardcoded json string that is read from a file.
I am doing something like this

r := Info{Ids: names, assignment: existingJsonString}
body, _ := json.Marshal(r)

However the above body is incorrect as assignment appears as string and not a json object. How can I tell the info struct that assignment will be a json string and not a regular string so that json.Marshal plays well with it ?

Use the type json.RawMessage, and please note that assignment should be exported:

type Info struct {
	Ids        []string        `json:"ids"`
	Assignment json.RawMessage `json:"assignment"`
}

Example:

package main

import (
	"encoding/json"
	"fmt"
)

type Info struct {
	Ids        []string        `json:"ids"`
	Assignment json.RawMessage `json:"assignment"`
}

func main() {
	r := Info{
		Ids:        []string{"id1", "id2"},
		Assignment: json.RawMessage(`{"a":1,"b":"str"}`),
	}
	body, err := json.Marshal(r)
	if err != nil {
		panic(err)
	}

	fmt.Printf("%s\n", body)
}