golang embedding of struct

user.go

package models

import "time"

type User struct {
	Id int64 `json:"id"`
	Name string `json:"name"`
	CreatedAt time.Time `json:"created_at"`
}

type UserEmbd struct {
	User
	CreatedAt string `json:"created_at"`
}

user_test.go

package models

import (
	"testing"
	"time"
	"encoding/json"
)

func TestUser_MarshalJSON(t *testing.T) {
	u := &User{
		Id:100,
		Name:"john",
		CreatedAt: time.Now(),
	}

	ue := &UserEmbd{
		User: *u,
		CreatedAt: "20101010",
	}

	t.Logf("%+v", u)
	t.Logf("%+v", ue)

	data, _ := json.Marshal(u)
	t.Logf("%+v", string(data))

	data, _ = json.Marshal(ue)
	t.Logf("%+v", string(data))
}

//  	user_test.go:21: &{Id:100 Name:john CreatedAt:2018-03-19 15:03:38.492922 +0800 CST m=+0.100586140}
//	user_test.go:22: &{User:{Id:100 Name:john CreatedAt:2018-03-19 15:03:38.492922 +0800 CST m=+0.100586140} CreatedAt:20101010}
//	user_test.go:25: {"id":100,"name":"john","created_at":"2018-03-19T15:03:38.492922+08:00"}
//	user_test.go:28: {"id":100,"name":"john","created_at":"20101010"}

//	UserEmbd可用于接口层，User用于内部逻辑