去解码json字符串

Question

discovered that go json decoding is a big pain in the butt so please help. Here's my json:

 {  
   "BTC_BCN":{  
      "id":7,
      "last":"0.00000156",
      "lowestAsk":"0.00000156",
      "highestBid":"0.00000155",
      "percentChange":"0.01960784",
      "baseVolume":"4920.84786257",
      "quoteVolume":"3016048494.19305944",
      "isFrozen":"0",
      "high24hr":"0.00000183",
      "low24hr":"0.00000145"
   },
   "BTC_BELA":{  
      "id":8,
      "last":"0.00008847",
      "lowestAsk":"0.00008848",
      "highestBid":"0.00008847",
      "percentChange":"-0.00405268",
      "baseVolume":"169.66498061",
      "quoteVolume":"1981232.44495809",
      "isFrozen":"0",
      "high24hr":"0.00008995",
      "low24hr":"0.00008120"
   }, ...
}

So I need to put that in a type that I created

//Crypto is the currency object
type Crypto struct {
    iso           string //this is the key (ex: BTC_BCN)
    id            int
    last          float64
    lowestAsk     float64
    highestBid    float64
    percentChange float64
    baseVolume    float64
    quoteVolume   float64
    isFrozen      int
    high24hr      float64
    low24hr       float64
}

and here is what I did so far, but I ended up with the keys in place and an empty value

func main() {
    // sendEmail("Some text")
    currencies := getCurrencies()
    if currencies == nil {
        return
    }
    fmt.Println(len(currencies))

}

func getCurrencies() map[string]Crypto {
    curList := make(map[string]Crypto)
    resp, err := http.Get("https://poloniex.com/public?command=returnTicker")
    // fmt.Println(err)
    if err != nil {
        sendEmail("Error getting data from poloniex " + err.Error())
        return nil
    }
    body, readErr := ioutil.ReadAll(resp.Body)
    reader := strings.NewReader(string(body))
    jsonErr := json.NewDecoder(reader).Decode(&curList)
    // fmt.Printf("curList is : %#v\n", curList)
    // fmt.Printf("body is : %s\n", string(body))
    if readErr != nil {
        fmt.Printf("readErr: %s\n", readErr.Error())
    }
    if jsonErr != nil {
        fmt.Printf("jsonErr: %s\n", jsonErr.Error())
    }
    for k, v := range curList {
        fmt.Println("k:", k, "v:", v)
    }
    defer resp.Body.Close()
    return curList
}

output:

k: BTC_MAID v: {0 0 0 0 0 0 0 0 0 0}
k: BTC_NOTE v: {0 0 0 0 0 0 0 0 0 0}
k: BTC_VRC v: {0 0 0 0 0 0 0 0 0 0}
k: BTC_DOGE v: {0 0 0 0 0 0 0 0 0 0}...

Please excuse my stupid question but I've spent days on it and I think I am missing something. Cheers.

Answer 1

//Crypto is the currency object
type Crypto struct {
    Iso           string //this is the key (ex: BTC_BCN)
    Id            int
    Last          string
    LowestAsk     string
    HighestBid    string
    PercentChange string
    BaseVolume    string
    QuoteVolume   string
    IsFrozen      int
    High24hr      string
    Low24hr       string
}

You need to to export the fields by capitalising first character. On top of that, your float64 datas are in type: string ,hence either you read as string or format before assign to object Crypto .

---

Updated:

As pointed by @skomp, you may use a tag to annotate the type you're receiving from json file.

type Crypto struct {
    CryptoKey
    Id            int
    Last          float64 `json:"last,string"`
    LowestAsk     float64 `json:"lowestAsk,string"`
    HighestBid    float64 `json:"highestBid,string"`
    PercentChange float64 `json:"percentChange,string"`
    BaseVolume    float64 `json:"baseVolume,string"`
    QuoteVolume   float64 `json:"quoteVolume,string"`
    IsFrozen      int
    High24hr      float64 `json:"high24hr,string"`
    Low24hr       float64 `json:"low24hr,string"`
}

Answer 2

You are trying to decode in to a map containing your crypto object. This is incorrect. Create the mappings in the struct definition like so:

type Crypto struct {
    iso           string  `json:"BTC_BCN"` //this is the key (ex: BTC_BCN)
    id            int     `json:"id"`
    last          float64 `json:"las"`
    ...
}

crypto := &Crypto{}
err = json.NewDecoder(reader).Decode(crypto)