golang number gets cut off after converting to interface

May 18, 2023

so I have a json with many fields and I am looping through it as suggested by
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}

>Solution :

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}