英文:
Go - Custom unmarshaler - string to float
问题
我消费一个第三方API，它以字符串形式给出价格，有三种类型：
//输入[{"id": "A", "price": "123"},{"id": "B", "price": "123.5"},{"id": "C", "price": ""}]//期望输出[A 123,B 123.5,C 0]
我知道我可以在我的结构体中添加,string部分，但这不能处理订单C。我在这个 GitHub问题中找到了一个关于int的问题。在那里有一个playground代码，我稍微修改了一下以适应我的需求。
如果我将其更改为float64而不是int，那么现在订单A的日志将为0。
json: cannot unmarshal string into Go struct field Order.price of type float64[{A 0}]
我认为代码中的if string(data) == '""' {部分将检查空字符串（订单C的情况），如果是空字符串，则设置为0。但是"123"不等于""。我理解自定义解组器的其余部分，除了下面的部分。有人可以指点我正确的方向吗？
p := (*float64)(foe)*p = f
完整代码也在这里
package mainimport ("encoding/json""fmt""strings")type StringToFloat float64type Order struct {Id string `json:"id"`Price StringToFloat `json:"price"`}func (foe *StringToFloat) UnmarshalJSON(data []byte) error {if string(data) == `""` {if foe != nil {*foe = 0}return nil}var f float64err := json.Unmarshal(data, &f)if err != nil {return err}p := (*float64)(foe)*p = freturn nil}func main() {jsonString := `[{"id": "A", "price": "123"},{"id": "B", "price": "123.5"},{"id": "C", "price": ""}]`var orders []Orderif err := json.NewDecoder(strings.NewReader(jsonString)).Decode(&orders); err != nil {fmt.Println(err)}fmt.Println(orders)}
编辑：评论@mkopriva
我调整了解组器：
func (foe *StringToFloat) UnmarshalJSON(data []byte) {fmt.Println(string(data))if string(data) == `""` {if foe != nil {*foe = 0}}n, err := strconv.ParseFloat(string(data), 64)if err != nil {fmt.Println(err)}*foe = StringToFloat(n)}
这给我输出：
json: cannot unmarshal string into Go struct field Order.price of type main.StringToFloat[{A 0} {B 0} {C 0}]```<details><summary>英文:</summary>I consume a 3th party API that gives me the price as a string, there are 3 flavours:
//Input
[
{"id": "A", "price": "123"},
{"id": "B", "price": "123.5"},
{"id": "C", "price": ""}
]
//Expected output
[
A 123,
B 123.5,
C 0
]
I know i can add the `,string` part inside my struct but this will not handle order C. I have found [this](https://github.com/golang/go/issues/26800) github issue where this question is asked about int's. In there there is a [playground](https://go.dev/play/p/nWl2toE2RAE) code that i altered a little bit to my needs.If i change this to float64 instead of int i get an error with the log of order A that is now 0.
json: cannot unmarshal string into Go struct field Order.price of type float64
[{A 0}]
I thought that this `if string(data) == '""' {` part of the code will check for the empty string (case order C) if so: set to 0. But `"123"` is not `""`. The rest of the custom unmarshaler i understand apart from the part below. Can someone point me to the right direction?
p := (*float64)(foe)
*p = f
**The full code** [Also here](https://go.dev/play/p/-_BArOztsOj)
package main
import (
"encoding/json"
"fmt"
"strings"
)
type StringToFloat float64
type Order struct {
Id string json:"id"
Price StringToFloat json:"price"
}
func (foe *StringToFloat) UnmarshalJSON(data []byte) error {
if string(data) == "" {
if foe != nil {
*foe = 0
}
return nil
}
var f float64err := json.Unmarshal(data, &f)if err != nil {return err}p := (*float64)(foe)*p = freturn nil
}
func main() {
jsonString := [
{"id": "A", "price": "123"},
{"id": "B", "price": "123.5"},
{"id": "C", "price": ""}
]
var orders []Order
if err := json.NewDecoder(strings.NewReader(jsonString)).Decode(&orders); err != nil {
fmt.Println(err)
}
fmt.Println(orders)
}
EDIT: comment @mkoprivaI adjusted the unmarshaler:
func (foe *StringToFloat) UnmarshalJSON(data []byte) {
fmt.Println(string(data))
if string(data) == "" {
if foe != nil {
*foe = 0
}
}
n, err := strconv.ParseFloat(string(data), 64)if err != nil {fmt.Println(err)}*foe = StringToFloat(n)
}
What gives me this output:
json: cannot unmarshal string into Go struct field Order.price of type main.StringToFloat
[{A 0} {B 0} {C 0}]
</details># 答案1**得分**: 1请稍等，我会为您翻译这段代码。<details><summary>英文:</summary>Try this```gopackage mainimport ("encoding/json""fmt""strconv""strings")type StringToFloat float64type Order struct {Id string `json:"id"`Price StringToFloat `json:"price"`}func (foe *StringToFloat) UnmarshalJSON(data []byte) error {if string(data) == "\"\"" {if foe != nil {*foe = 0}return nil}num := strings.ReplaceAll(string(data), "\"", "")n, err := strconv.ParseFloat(num, 64)if err != nil {return err}*foe = StringToFloat(n)return nil}func main() {jsonString := `[{"id": "A", "price": "123"},{"id": "B", "price": "123.5"},{"id": "C", "price": ""}]`var orders []Orderif err := json.NewDecoder(strings.NewReader(jsonString)).Decode(&orders); err != nil {fmt.Println(err)}fmt.Println(orders)}```Go playground: https://go.dev/play/p/cHjNQ447eX9Things to note:- The function signature of UmarshalJSON func needs to be exactly the same as given to be picked up by Decode. In your updated code `error` return type was missing- `string(data)` gives `"123"` so the quotes need to be removed before `ParseFloat`- `return nil` is required after string = `""` check so it dosent go further</details>
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