json.Unmarshal nested object into string or []byte

Question

I'm trying to Unmarshal some json so that a nested object does not get parsed but just treated as a string or []byte.

So I want to get the following:

{     "id"  : 15,     "foo" : { "foo": 123, "bar": "baz" } } 

Unmarshaled into:

type Bar struct {     ID  int64  `json:"id"`     Foo []byte `json:"foo"` } 

I get the following error:

json: cannot unmarshal object into Go value of type []uint8 

playground demo

Answer 1

I think what you are looking for is the RawMessage type in the encoding/json package.

The documentation states:

type RawMessage []byte

RawMessage is a raw encoded JSON object. It implements Marshaler and Unmarshaler and can be used to delay JSON decoding or precompute a JSON encoding.

Here is a working example of using RawMessage:

package main  import (     "encoding/json"     "fmt" )  var jsonStr = []byte(`{     "id"  : 15,     "foo" : { "foo": 123, "bar": "baz" } }`)  type Bar struct {     Id  int64           `json:"id"`     Foo json.RawMessage `json:"foo"` }  func main() {     var bar Bar      err := json.Unmarshal(jsonStr, &bar)     if err != nil {         panic(err)     }     fmt.Printf("%+v\n", bar) } 

Output:

{Id:15 Foo:[123 32 34 102 111 111 34 58 32 49 50 51 44 32 34 98 97 114 34 58 32 34 98 97 122 34 32 125]}

Playground