是否可以部分解码和更新JSON？ （走）

Question

I need to decode and update only a specific value of a json object. The issue is that I don't know the full structure of the object. The encoding/json package "ignores"/truncates the fields not provided in the struct so on encoding these fields are lost. I'm wondering if it's possible to unmarshal only the structure I know, update it and then marshal it without to truncate/remove the unknown structure/information.

Answer 1

It seems it's possible.

package main

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

func main() {
    type Color struct {
        Space string
        Point json.RawMessage // delay parsing until we know the color space
    }
    type RGB struct {
        R uint8
        G uint8
        B uint8
    }
    type YCbCr struct {
        Y  uint8
        Cb int8
        Cr int8
    }

    var j = []byte(`
        {"Space": "YCbCr", "Point": {"Y": 255, "Cb": 0, "Cr": -10}}`)
    var colors Color
    err := json.Unmarshal(j, &colors)
    if err != nil {
        log.Fatalln("error:", err)
    }
    colors.Space = "no-space"

    b, err := json.Marshal(&colors)
    if err != nil {
        panic(err)
    }
    fmt.Printf("b is now %s", b)
    return

}