Partly JSON unmarshal into a map in Go

Question

My websocket server will receive and unmarshal JSON data  This data will always be wrapped in an object with key value pairs  The key-string will act as value identifier  telling the Go server what kind of value it is  By knowing what type of value  I can then proceed to JSON unmarshal the value into the correct type of struct   Each json-object might contain multiple key value pairs   Example JSON          sendMsg    user   ANisus   msg   Trying to send a message         say   Hello      Is there any easy way using the  encoding json  package to do this   package main  import        encoding json       fmt        the struct for the value of a  sendMsg -command type sendMsg struct       user string     msg  string      The type for the value of a  say -command type say string  func main        data      byte    sendMsg    user   ANisus   msg   Trying to send a message    say   Hello             This won t work because json MapObject   byte  doesn t exist     objmap  err    json MapObject data          This is what I wish the objmap to contain       var objmap   map string   byte            sendMsg     byte    user   ANisus   msg   Trying to send a message               say     byte   hello                 fmt Printf   v   objmap      Thanks for any kind of suggestion help

User · Accepted Answer

This can be accomplished by Unmarshaling into a map[string]json.RawMessage.

var objmap map[string]json.RawMessage
err := json.Unmarshal(data, &objmap)

To further parse sendMsg, you could then do something like:

var s sendMsg
err = json.Unmarshal(objmap["sendMsg"], &s)

For say, you can do the same thing and unmarshal into a string:

var str string
err = json.Unmarshal(objmap["say"], &str)

EDIT: Keep in mind you will also need to export the variables in your sendMsg struct to unmarshal correctly. So your struct definition would be:

type sendMsg struct {
    User string
    Msg  string
}

Example: https://play.golang.org/p/OrIjvqIsi4-

User · Answer

Further to Stephen Weinberg s answer  I have since implemented a handy tool called iojson  which helps to populate data to an existing object easily as well as encoding the existing object to a JSON string  A iojson middleware is also provided to work with other middlewares  More examples can be found at https   github com junhsieh iojson  Example   func main         jsonStr       Status  true  ErrArr      ObjArr     Name   My luxury car   ItemArr     Name   Bag     Name   Pen       ObjMap            car    NewCar        i    iojson NewIOJSON        if err    i Decode strings NewReader jsonStr    err    nil           fmt Printf  err   s n   err Error                  populating data to a live car object      if v  err    i GetObjFromArr 0  car   err    nil           fmt Printf  err   s n   err Error          else           fmt Printf  car  original    s n   car GetName            fmt Printf  car  returned    s n   v   Car  GetName             for k  item    range car ItemArr               fmt Printf  ItemArr  d  of car  original    s n   k  item GetName                       for k  item    range v   Car  ItemArr               fmt Printf  ItemArr  d  of car  returned    s n   k  item GetName                        Sample output   car  original   My luxury car car  returned   My luxury car ItemArr 0  of car  original   Bag ItemArr 1  of car  original   Pen ItemArr 0  of car  returned   Bag ItemArr 1  of car  returned   Pen

User · Answer

Here is an elegant way to do similar thing  But why do partly JSON unmarshal  That doesn t make sense    Create your structs  for the Chat  Decode json to the Struct  Now you can access everything in Struct Object easily     Look below at the working code  Copy and paste it   import       bytes      encoding json     Encoding and Decoding Package     fmt      var messeging       say   Hello    sendMsg         user   ANisus        msg   Trying to send a message           type SendMsg struct      User string  json  user      Msg  string  json  msg       type Chat struct      Say     string    json  say      SendMsg  SendMsg  json  sendMsg      func main           Clean way to solve Json Decoding in Go          Excellent solution        var chat Chat    r    bytes NewReader   byte messeging      chatErr    json NewDecoder r  Decode  amp chat     errHandler chatErr     fmt Println chat Say     fmt Println chat SendMsg User     fmt Println chat SendMsg Msg       func errHandler err error       if err    nil        fmt Println err       return           Go playground

[json] Partly JSON unmarshal into a map in Go

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