Marshal JSON in Golang using common lower-snake-case object key conventions

conventional-json.go

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"regexp"
	"time"
)

// Regexp definitions
var keyMatchRegex = regexp.MustCompile(`\"(\w+)\":`)
var wordBarrierRegex = regexp.MustCompile(`(\w)([A-Z])`)

type conventionalMarshaller struct {
	Value interface{}
}

func (c conventionalMarshaller) MarshalJSON() ([]byte, error) {
	marshalled, err := json.Marshal(c.Value)

	converted := keyMatchRegex.ReplaceAllFunc(
		marshalled,
		func(match []byte) []byte {
			return bytes.ToLower(wordBarrierRegex.ReplaceAll(
				match,
				[]byte(`${1}_${2}`),
			))
		},
	)

	return converted, err
}

type exampleModel struct {
	Title       string
	Description string
	CreatedAt   time.Time
	UpdatedAt   time.Time
	IsActive    bool
}

func main() {
	model := exampleModel{
		Title:       "Example Title",
		Description: "whatever",
		CreatedAt:   time.Now(),
		UpdatedAt:   time.Now(),
		IsActive:    true,
	}

	encoded, _ := json.MarshalIndent(conventionalMarshaller{model}, "", "  ")

	fmt.Println(string(encoded))
}

Output

{
  "title": "Example Title",
  "description": "whatever",
  "created_at": "2015-11-17T20:43:31.046357698-05:00",
  "updated_at": "2015-11-17T20:43:31.046359788-05:00",
  "is_active": true
}

How about "is_ur_l" for "IsURL" field? Or "is_ur_lactive" for "IsURLActive"?
I expected to have "is_url" and "is_url_active" respectively.

@bezigon Maybe that's also work.

(\w)([A-Z]) -> ([a-z_0-9])([A-Z])

This is actually outputting snake case, I've uploaded a gist giving lower camel case here https://gist.github.com/piersy/b9934790a8892db1a603820c0c23e4a7

Soooo, I know its been 3+ years and all, but I've turned this kind of behavior into a proper package:
https://github.com/Rican7/conjson

It incorporates both snake_case and camelCase transformations, among others. 😃

Thanks for the comments, suggestions, and forks on this original Gist everyone!

☝️ /cc: @bezigon @edwardstudy @glassonion1 @piersy @JoeyBoolean

☝️ /cc: @bezigon @edwardstudy @glassonion1 @piersy @JoeyBoolean

(re-doing this since people actually get notified now... https://help.github.com/en/articles/about-gists#receiving-notifications-for-gist-activity)

Nice, thx !
It works very well.

I just change your regex for (\w{2,})([A-Z]).

I have interface with the key ID and your regex transform this in i_d
If someone has a better way :)

@Nyura95 try checking out this project instead:
https://github.com/Rican7/conjson

It's an expansion on this idea. 😃

Nice ! Thank you for sharing !