Demystifying Go’s JSON Marshaling With Embedded Structs

Go, a statically typed, compiled programming language designed at Google, has become a popular choice for various applications due to its simplicity and efficiency. One area where Go really shines is in handling JSON data.

Today, we will explore an interesting aspect of Go’s JSON marshaling, specifically when dealing with embedded structs. We will use a simple Event a struct that has an Id of type int and an embedded time.Time struct.

Here’s the code snippet:

package main

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

func main() {
 type Event struct {
  Id int
  time.Time
 }

 event := Event{
  Id:   1234,
  Time: time.Now(),
 }

 b, _ := json.Marshal(event)
 fmt.Print(string(b))
}

This program defines an Event type with an Id field and a time.Time field creates an instance of Event, and then attempts to marshal it into a JSON object.

If we run this program, we might be surprised by the output:

"2009-11-10T23:00:00Z"

The Id field is missing! Why is that?

Understanding Embedded Structs in Go

In Go, when we include a type within another type without giving it a name, it’s called an embedded struct. The methods, and fields of the embedded struct become part of the outer struct. However, when it comes to marshaling to JSON, Go’s encoding/json package treats embedded fields differently.