在golang中将字符串转换为json，反之亦然？

Question

In my app, I receive a json from the client. This json can be anything since the user defines the keys and the values. In the backend I store it as string in the datastore.

Now i'm trying to override the MarshalJson / UnmarshalJson functions so that what I send / receive from the client is not a string but a json.

I can't figure out how to convert a string to json in go.

my structure

type ContextData string
type Iot struct {
Id              IotId       `json:"id,string" datastore:"-" goon:"id"`
Name            string   `json:"name"`
Context         ContextData  `json:"context" datastore:",noindex"` }

example of received data

{ 'id' : '',
  'name' '',
  'context': {
           'key1': value1,
           'key2': value2 }}

how i want to store this Context field in the datastore as a noindex string '{'key1':value1, 'key2':value2}' example of data i want to send

{ 'id' : '',
  'name' '',
  'context': {
           'key1': value1,
           'key2': value2 }}

Answer 1

If I understand your problem correctly, you want to use json.RawMessage as Context.

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.

RawMessage is just []byte, so you can keep it in data store and then attach it for an outgoing messages as "precomputed JSON".

type Iot struct {
    Id      int             `json:"id"`
    Name    string          `json:"name"`
    Context json.RawMessage `json:"context"` // RawMessage here! (not a string)
}

func main() {
    in := []byte(`{"id":1,"name":"test","context":{"key1":"value1","key2":2}}`)

    var iot Iot
    err := json.Unmarshal(in, &iot)
    if err != nil {
        panic(err)
    }

    // Context is []byte, so you can keep it as string in DB
    fmt.Println("ctx:", string(iot.Context))

    // Marshal back to json (as original)
    out, _ := json.Marshal(&iot)
    fmt.Println(string(out))
}

https://play.golang.org/p/69n0B2PNRv