go "encoding/json" : marshal json field - json

Question

I have a PostgreSQL schema with json field's (DisplayInfo, and FormatInfo). Structure of this field's is dynamic.
I'can read and render it only as string (string type in render struct) :
[
{
"ID":9,
"Name":"120 №1",
"DisplayInfo":"{\"path\": \"http://path/to/img.png\"}",
"Format":{
"Code":"frame-120",
"Width":120,
"Height":60,
"FormatInfo":"[{\"name\": \"\\u0413\\u043b\\u0430\\u0432\\u043d\\u043e\\u0435 \\u0438\\u0437\\u043e\\u0431\\u0440\\u0430\\u0436\\u0435\\u043d\\u0438\\u0435\", \"field_type\": \"img\", \"key\": \"path\"}]"
},
"Weight":0.075,
"Application":8,
"Url":"//path/to/game",
"Referrer":""
}
]
but i want output field DisplayInfo as JSON object. How ?
My render code:
func renderJSON(w http.ResponseWriter, obj models.Model) {
js, err := json.Marshal(obj)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
w.Header().Set("Content-Type", "application/json; charset=utf-8")
w.Header().Set("Access-Control-Allow-Origin", "*")
w.Write(js)
}
UPD 1 : Structure of this field's is dynamic. DisplayInfo may have 'path' field, or may not. They may have additional fields.
UPD 2. I wana output DisplayInfo and FormatInfo as json-object(not string), as part of whole object, like this:
[
{
"ID":9,
"Name":"120 №1",
"DisplayInfo":{"path": "http://path/to/img.png"},
"Format":{
"Code":"frame-120",
"Width":120,
"Height":60,
"FormatInfo":[{"name": "\\u0413\\u043b\\u0430\\u0432\\u043d\\u043e\\u0435 \\u0438\\u0437\\u043e\\u0431\\u0440\\u0430\\u0436\\u0435\\u043d\\u0438\\u0435", "field_type": "img", "key": "path"}]
},
"Weight":0.075,
"Application":8,
"Url":"//path/to/game",
"Referrer":""
}
]
UPD 3: Structures
Actual structure is :
type BannerSerializer struct {
ID int
Name string
DisplayInfo string
Format formatSerializer
Weight float32
Application int
Url string
Referrer string
}
Then i trying this structure:
type BannerSerializer struct {
ID int
Name string
DisplayInfo json.RawMessage
Format formatSerializer
Weight float32
Application int
Url string
Referrer string
}
DisplayInfo serialize as base64 string (or like base64, don't know)

Answer 1

Use a pointer to json.RawMessage:
type Data struct {
Obj *json.RawMessage
}
Playground: http://play.golang.org/p/Qq9IUBDLzJ.

Answer 2

Assuming you have access to change models.Model, you can create your own type with a custom Unmarshaler that just returns the raw string:
type JSONString string
func (s JSONString) MarshalJSON() ([]byte, error) {
return []byte(s), nil
}
Working example:
package main
import (
"encoding/json"
"fmt"
)
type JSONString string
func (s JSONString) MarshalJSON() ([]byte, error) {
return []byte(s), nil
}
type Model struct {
ID int
Name string
DisplayInfo JSONString
}
func main() {
data := []byte(`{
"ID":9,
"Name":"120 №1",
"DisplayInfo":"{\"path\": \"http://path/to/img.png\"}"
}`)
var obj Model
err := json.Unmarshal(data, &obj)
if err != nil {
panic(err)
}
// Here comes your code
js, err := json.Marshal(obj)
if err != nil {
panic(err)
}
fmt.Println(string(js))
}
Output:
{"ID":9,"Name":"120 №1","DisplayInfo":{"path":"http://path/to/img.png"}}
Playground: http://play.golang.org/p/6bcnuGjlU8

Answer 3

You'd have to unmarshal it, here's an example:
var data []*struct {
ID int
DisplayInfo string
}
if err := json.Unmarshal([]byte(j), &data); err != nil {
log.Fatal(err)
}
for _, d := range data {
var displayInfo struct{ Path string }
if err := json.Unmarshal([]byte(d.DisplayInfo), &displayInfo); err != nil {
log.Fatal(err)
}
fmt.Println(d.ID, displayInfo.Path)
}
playground