In Go Language, how do I unmarshal json to array of object?

Question

I have the following JSON, and I want to parse it into array of class:

{
    \"1001\": {\"level\":10, \"monster-id\": 1001, \"skill-level\": 1, \"aimer-id\":         


        

Answer 1

Slightly off to one side - you asked for an array of objects when you needed a map

If you need an array (actually a slice)

http://ioblocks.blogspot.com/2014/09/loading-arrayslice-of-objects-from-json.html

Answer 2

This code has many errors in it. To start with, the json isn't valid json. You are missing the commas in between key pairs in your top level object. I added the commas and pretty printed it for you:

{
   "1001":{
      "level":10,
      "monster-id":1001,
      "skill-level":1,
      "aimer-id":301
   },
   "1002":{
      "level":12,
      "monster-id":1002,
      "skill-level":1,
      "aimer-id":302
   },
   "1003":{
      "level":16,
      "monster-id":1003,
      "skill-level":2,
      "aimer-id":303
   }
}

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Your next problem (the one you asked about) is that m := data.(map[string]interface{}) makes m a map[string]interface{}. That means when you index it such as the v in your range loop, the type is interface{}. You need to type assert it again with v.(map[string]interface{}) and then type assert each time you read from the map.

---

I also notice that you next attempt mc.Pool[i] = monster when i is an int and mc.Pool is a map[string]Monster. An int is not a valid key for that map.

---

Your data looks very rigid so I would make unmarshall do most of the work for you. Instead of providing it a map[string]interface{}, you can provide it a map[string]Monster.

Here is a quick example. As well as changing how the unmarshalling works, I also added an error return. The error return is useful for finding bugs. That error return is what told me you had invalid json.

type Monster struct {
    MonsterId  int32 `json:"monster-id"`
    Level      int32 `json:"level"`
    SkillLevel int32 `json:"skill-level"`
    AimerId    int32 `json:"aimer-id"`
}

type MonsterCollection struct {
    Pool map[string]Monster
}

func (mc *MonsterCollection) FromJson(jsonStr string) error {
    var data = &mc.Pool
    b := []byte(jsonStr)
    return json.Unmarshal(b, data)
}

I posted a working example to goplay: http://play.golang.org/p/4EaasS2VLL