解码JSON值的更好方法

Question

Assume a JSON object with the general format

  "accounts": [
    {
      "id": "<ACCOUNT>", 
      "tags": []
    }
  ]
}

I can create a struct with corresponding json tags to decode it like so

 type AccountProperties struct {
    ID AccountID `json:"id"`
    MT4AccountID int `json:"mt4AccountID,omitempty"`
    Tags []string `json:"tags"`
  }

  type Accounts struct {
    Accounts []AccountProperties `json:"accounts"`
  }

But the last struct with just one element seems incorrect to me. Is there a way I could simply say type Accounts []AccountProperties `json:"accounts"` instead of creating an entire new struct just to decode this object?

Answer 1

You need somewhere to store the json string accounts. Using a:

var m map[string][]AccountProperties

suffices, though of course you then need to know to use the string literal accounts to access the (single) map entry thus created:

type AccountProperties struct {
    ID           string   `json:"id"`
    MT4AccountID int      `json:"mt4AccountID,omitempty"`
    Tags         []string `json:"tags"`
}

func main() {
    var m map[string][]AccountProperties
    err := json.Unmarshal([]byte(data), &m)
    fmt.Println(err, m["accounts"])
}

See complete Go Playground example (I had to change the type of ID to string and fix the missing { in the json).

---

As Dave C points out in comments, this is no shorter than just using an anonymous struct type:

var a struct{ Accounts []AccountProperties }

in terms of the Unmarshall call (and when done this way it's more convenient to use). Should you want to use an anonymous struct like this in a json.Marshall call, you'll need to tag its single element to get a lowercase encoding: without a tag it will be called "Accounts" rather than "accounts".

(I don't claim the map method to be better, just an alternative.)