在不涉及所有字段的情况下封送和封送JSON正文

Question

I'm looking for a way to unmarshal a JSON body without having to specify targets for all fields. And then be a able to "remarshal" the body with implicit fields untouched.

Something like this would be good, but doesn't work as a expected: (https://play.golang.org/p/fnVOKrmiFj)

package main

import (
    "encoding/json"
    "fmt"
)

type Transaction struct {
    Field1  string                  `json:"field1"`
    X       map[string]interface{}  `json:"-"`
}

func main() {
    body := []byte(`{"field1": "value1", "field2": "value2"}`)
    fmt.Printf("%+v
", string(body))

    var unmarshalledTransaction Transaction
    json.Unmarshal(body, &unmarshalledTransaction)
    fmt.Printf("%+v
", unmarshalledTransaction)

    remarshalledTransaction, _ := json.Marshal(&unmarshalledTransaction)
    fmt.Printf("%+v
", string(remarshalledTransaction))    
}

Gives the output

{"field1": "value1", "field2": "value2"}
{Field1:value1 X:map[]}
{"field1":"value1"}

My expected result would be that unmarshalledTransaction contains the "leftover" fields in the X fields. And they are then restored when Marshalling again.

Can this be done?

Answer 1

You would need to implement the MarshalJSON and UnmarshalJSON interfaces, and write your own logic to remap the fields to the appropriate spots:

func (t *Transaction) MarshalJSON() ([]byte, error) {
    data := t.X
    data["field1"] = t.Field1
    return json.Marshal(data)
}

func (t *Transaction) UnmarshalJSON(data []byte) error {
    m := make(map[string]interface{})
    json.Unmarshal(data, &m)
    t.Field1 = m["field1"].(string)
    delete(m, "field1")
    t.X = m
    return nil
}

https://play.golang.org/p/KBGAsXB0xA