英文:
JSON number gets cut off after unmarshaling to interface
问题
所以我有一个包含许多字段的JSON，我按照https://stackoverflow.com/questions/66893640/how-effectively-to-change-json-keys中的建议进行循环遍历，以删除我不需要的一些键。但是在删除之后，现有JSON的原始值发生了变化，其中一些似乎是浮点数，我制作了一个演示来展示这一点。
我该如何改变这种行为？是interface{}引起了这个问题吗？为什么1684366653200744506被截断为1684366653200744400？
谢谢！
https://go.dev/play/p/X2auWqWB2fL
供参考，输出的JSON已更改为1684366653200744400
2009/11/10 23:00:00 1684366653200744448.000000
2009/11/10 23:00:00 map[timestamp:1.6843666532007444e+18]
2009/11/10 23:00:00 json Marshal from maps of key string and value interface to batch json for insert to DB
2009/11/10 23:00:00 {"timestamp":1684366653200744400}
英文:
So I have a JSON with many fields and I am looping through it as suggested by
https://stackoverflow.com/questions/66893640/how-effectively-to-change-json-keys
to delete some of the keys I don't need. But after deletion, the original values of the existing JSON was changed, some of them are float numbers it seems and I made a demo to show it.
How can I change this behavior? Is the interface{} causing the issue? Why is 1684366653200744506 cut off to 1684366653200744400?
Thanks!
https://go.dev/play/p/X2auWqWB2fL
For reference, the output JSON is changed to 1684366653200744400
2009/11/10 23:00:00 1684366653200744448.000000
2009/11/10 23:00:00 map[timestamp:1.6843666532007444e+18]
2009/11/10 23:00:00 json Marshal from maps of key string and value interface to batch json for insert to DB
2009/11/10 23:00:00 {"timestamp":1684366653200744400}
答案1
得分: 2
我建议创建一个类型并删除你不需要的字段。
package main
import (
"encoding/json"
"log"
)
type A struct {
Timestamp int64 `json:"timestamp"`
}
func main() {
jsonBatch := `{"timestamp":1684366653200744506, "todelete":"string value or boolean value"}`
i := A{}
if err := json.Unmarshal([]byte(jsonBatch), &i); err != nil {
log.Println("从批处理JSON解组失败")
log.Println(err)
}
dbJsonBatch, err := json.Marshal(i)
if err != nil {
log.Println("将键为字符串和值为接口的映射组合成批处理JSON以插入到数据库中失败")
log.Println(err)
}
log.Println("将键为字符串和值为接口的映射组合成批处理JSON以插入到数据库中")
log.Println(string(dbJsonBatch))
}
这将打印：
2009/11/10 23:00:00 将键为字符串和值为接口的映射组合成批处理JSON以插入到数据库中
2009/11/10 23:00:00 {"timestamp":1684366653200744506}
英文:
I suggest creating a type and removing the field you don't need.
package main
import (
"encoding/json"
"log"
)
type A struct {
Timestamp int64 `json:"timestamp"`
}
func main() {
jsonBatch := `{"timestamp":1684366653200744506, "todelete":"string value or boolean value"}`
i := A{}
if err := json.Unmarshal([]byte(jsonBatch), &i); err != nil {
log.Println("json UnMarshal from batch json failed")
log.Println(err)
}
dbJsonBatch, err := json.Marshal(i)
if err != nil {
log.Println("json Marshal from batch json failed")
log.Println(err)
}
log.Println("json Marshal from maps of key string and value interface to batch json for insert to DB")
log.Println(string(dbJsonBatch))
}
This prints
2009/11/10 23:00:00 json Marshal from maps of key string and value interface to batch json for insert to DB
2009/11/10 23:00:00 {"timestamp":1684366653200744506}
答案2
得分: 2
这是因为默认情况下，encoding/json 包将 JSON 数字存储为接口值中的 float64 类型。可以参考 json.Unmarshal：
> 为了将 JSON 解组成接口值，Unmarshal 将以下类型之一存储在接口值中：
> - 布尔值，用于 JSON 布尔值
> - float64，用于 JSON 数字
> - ...
你可以创建一个解码器并调用 (*Decoder).UseNumber 来改变这种行为：
jsonBatch := `{"timestamp":1684366653200744506, "todelete":"string value or boolean value"}`
dec := json.NewDecoder(strings.NewReader(jsonBatch))
dec.UseNumber()
var i interface{}
if err := dec.Decode(&i); err != nil {
参考链接：https://go.dev/play/p/ZjWB-NfiEQL。
英文:
It's because by default, the encoding/json package stores float64 in the interface value for JSON numbers. See json.Unmarshal:
> To unmarshal JSON into an interface value, Unmarshal stores one of these in the interface value:
> - bool, for JSON booleans
> - float64, for JSON numbers
> - ...
You can create a decoder and call (*Decoder).UseNumber to change the behavior:
jsonBatch := `{"timestamp":1684366653200744506, "todelete":"string value or boolean value"}`
dec := json.NewDecoder(strings.NewReader(jsonBatch))
dec.UseNumber()
var i interface{}
if err := dec.Decode(&i); err != nil {
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