Unmarshaling json into a type - go

Question

I get the following data:
{
"timestamp": "1526058949",
"bids": [
[
"7215.90",
"2.31930000"
],
[
"7215.77",
"1.00000000"
]
]
}
via websocket and I would like to unmarshall it into
type OrderBookItem struct {
Price string
Amount string
}
type OrderBookResult struct {
Timestamp string `json:"timestamp"`
Bids []OrderBookItem `json:"bids"`
Asks []OrderBookItem `json:"asks"`
}
Unmarshal it with:
s := e.Data.(string)
d := &OrderBookResult{}
err := json.Unmarshal([]byte(s), d)
if err == nil {
....
} else {
fmt.Println(err.Error())
}
But I keep getting the error:
json: cannot unmarshal string into Go struct field
OrderBookResult.bids of type feed.OrderBookItem
When I change the struct into
type OrderBookResult struct {
Timestamp string `json:"timestamp"`
Bids [][]string `json:"bids"`
Asks [][]string `json:"asks"`
}
it works. I would like them to be defined as float64 which is what they are. What do I have to change?

Answer 1

As the error says:
json: cannot unmarshal string into Go struct field
OrderBookResult.bids of type feed.OrderBookItem
We cannot convert OrderBookResult.bids which is a slice of string into OrderBookItem which is struct
Implement UnmarshalJSON interface to convert array into objects for price and amount of OrderBookItem struct. Like below
package main
import (
"fmt"
"encoding/json"
)
type OrderBookItem struct {
Price string
Amount string
}
func(item *OrderBookItem) UnmarshalJSON(data []byte)error{
var v []string
if err:= json.Unmarshal(data, &v);err!=nil{
fmt.Println(err)
return err
}
item.Price = v[0]
item.Amount = v[1]
return nil
}
type OrderBookResult struct {
Timestamp string `json:"timestamp"`
Bids []OrderBookItem `json:"bids"`
Asks []OrderBookItem `json:"asks"`
}
func main() {
var result OrderBookResult
jsonString := []byte(`{"timestamp": "1526058949", "bids": [["7215.90", "2.31930000"], ["7215.77", "1.00000000"]]}`)
if err := json.Unmarshal([]byte(jsonString), &result); err != nil{
fmt.Println(err)
}
fmt.Printf("%+v", result)
}
Playground working example
For more information read GoLang spec for Unmarshaler

Answer 2

You are treating your bids as a structure of two separate strings, when they are really a slice of strings in the JSON. If you change OrderBookItem to be
type OrderBookItem []string
which is how you have defined them in the second bit, which works.
To access the values you just have to do:
price := d.Bids[0]
amount := d.Bids[1]