douwen2072 2015-12-15 14:40
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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 }}
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3条回答 默认 最新

  • dop2144 2015-12-15 17:25

    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 {
        // 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)

    本回答被题主选为最佳回答 , 对您是否有帮助呢?



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