如何在Golang中正确解组无键JSON数组？

Question

I have JSON data which looks like this:

[
  {
    "globalTradeID": 64201000,
    "tradeID": 549285,
    "date": "2016-11-11 23:51:58",
    "type": "buy",
    "rate": "10.33999779",
    "amount": "0.02176472",
    "total": "0.22504715"
  },
  {
    "globalTradeID": 64200631,
    "tradeID": 549284,
    "date": "2016-11-11 23:48:39",
    "type": "buy",
    "rate": "10.33999822",
    "amount": "0.18211700",
    "total": "1.88308945"
  }...
]

I've tried to unmarshall this JSON by defining a type:

type TradeHistoryResponse   []TradeHistoryInfo

type TradeHistoryInfo struct {
    GlobalTradeID   int64   `json:"globalTradeID"`
    TradeID         int64   `json:"tradeID"`
    Date            string  `json:"date"`
    Type            string  `json:"type"`
    Rate            float64 `json:"rate,string"`
    Amount          float64 `json:"amount,string"`
    Total           float64 `json:"total,string"`
}

And then pulling the JSON data as so:

    //Read response
    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        return nil, fmt.Errorf("[Poloniex] (doRequest) Failed to parse response for query to %s! (%s)", reqURL, err.Error())
    } 

    //Convert JSON to struct

    var THR TradeHistoryResponse
    err = json.Unmarshal(body, &THR)
    if err != nil {
        return nil, fmt.Errorf("[Poloniex] (doRequest) Failed to convert response into JSON for query to %s! (%s)", reqURL, err.Error())
    }

I get the following error:

(json: cannot unmarshal object into Go value of type poloniex.TradeHistoryResponse)

My best guess why the Unmarshall doesn't work is because the array is key-less?

Would love to have some clarification on the matter on how I might best get this working.

Answer 1

I didn't think unmarhsalling an array in a JSON like you intended actually works but to the props of encoding/json it does. Example code: package main

import (
    "encoding/json"
    "fmt"
    "log"
)

var mjs string = "[" +
    "{" +
    `"globalTradeID": 64201000,
                          "tradeID": 549285,
                          "date": "2016-11-11 23:51:58",
                          "type": "buy",
                          "rate": "10.33999779",
                          "amount": "0.02176472",
                          "total": "0.22504715"
                        },
                        {
                          "globalTradeID": 64200631,
                          "tradeID": 549284,
                          "date": "2016-11-11 23:48:39",
                          "type": "buy",
                          "rate": "10.33999822",
                          "amount": "0.18211700",
                          "total": "1.88308945"
                        }
                        ]`

type TradeHistoryResponse []TradeHistoryInfo

type TradeHistoryInfo struct {
    GlobalTradeID int64   `json:"globalTradeID"`
    TradeID       int64   `json:"tradeID"`
    Date          string  `json:"date"`
    Type          string  `json:"type"`
    Rate          float64 `json:"rate,string"`
    Amount        float64 `json:"amount,string"`
    Total         float64 `json:"total,string"`
}

func main() {

    //Convert JSON to struct

    var THR TradeHistoryResponse
    err := json.Unmarshal([]byte(mjs), &THR)
    if err != nil {
    log.Fatal(err)
    }
  for _, v := range THR {
    fmt.Printf("%+v", v)
    fmt.Printf("
")
  }
}

This prints out all the values as expected. So it doesn't have a problem converting the json values to float/int either (which would have been my second guess).

Are you sure you aren't modifying the Body in any way ? And that the example you give cover all edge cases ?

Could you add:

fmt.Println(string(body)) 

to the second error block and log the error it give here.

Also what version of go are you using ? I wouldn't exclude the possibility of encoding/json to have changed between versions. In the end, if this is indeed the case the easy fix would be taking your response as a string, removing all whitespaces and splitting at "}'{" as in:

fmtBody := strings.Replace(string(body), "
", "", -1)
fmtBody = strings.Replace(string(fmtBody), "\w", "", -1)
fmtBody = strings.Replace(string(fmtBody), "[", "", -1)
fmtBody = strings.Replace(string(fmtBody), "]", "", -1)
var goArrOfYourJsonsObj []String = strings.Split(fmtBody, "},{")
for k, _ := range goArrOfYourJsonsObj {
  goArrOfYourJsonsObj[k] += "}"
}

And now you have your JSON objects neatly separated into a go array of types String which, can be used in Unmarshall as []byte(val).