Nested Go Structs for JSON marshaling with optional structs - json

Question

I'm trying to initialize a nested struct to then marshal into json for an API response. The challenge I'm hitting is one of the components (a slice of structs) can have n number of members but of one of two possible types (text, image).
The JSON I want to create looks like this:
{
"messages": [
{
"message_parts": [
{
"text": {
"content": "dfdffd"
}
},
{
"image": {
"url": "https://image.jpg"
}
}
],
"actor_id": "44444444",
"actor_type": "agent"
}
],
"channel_id": "44444444",
"users": [
{
"id": "44444444"
}
]
}
In the message_parts slice, that can contain at least one of text or image but possibly one of each.
My structs look like this currently:
Type messagePayload struct {
Messages []Messages `json:"messages"`
Status string `json:"status,omitempty"`
ChannelID string `json:"channel_id"`
Users []Users `json:"users"`
}
type Messages struct {
MessageParts []MessageParts `json:"message_parts"`
ActorID string `json:"actor_id"`
ActorType string `json:"actor_type"`
}
type Users struct {
ID string `json:"id"`
}
type Text struct {
Content string `json:"content,omitempty"`
}
type MessageParts struct {
Text *Text `json:"text,omitempty"`
Image *Image `json:"image,omitempty"`
}
type Image struct {
URL string `json:"url,omitempty"`
}
I'm really struggling to initialize this in a way that not show up in the json if they're not present.
here's where I'm at but it obviously doesn't work:
payload := &messagePayload{
Messages: []Messages{
{
MessageParts: []MessageParts{
{
&Text{
Content: text,
},
},
{
&Image{
URL: mediaurl,
},
},
},
ActorID: agentID,
ActorType: "agent",
}},
ChannelID: channelid,
Users: []Users{
{
ID: user,
},
},
}
EDIT:
Thanks to hint below and a few other findings, I've found the best way is to initalize the payload and then add the slices for text and images as needed:
https://play.golang.org/p/Pmmv00spcI6

Answer 1

As noted above, I was able to find a solution- you need to initialize the payload without the text or image data, then append them to the MessageParts slice:
package main
import (
"encoding/json"
"fmt"
)
type messagePayload struct {
Messages []Messages `json:"messages"`
Status string `json:"status,omitempty"`
ChannelID string `json:"channel_id"`
Users []Users `json:"users"`
}
type Messages struct {
MessageParts []MessageParts `json:"message_parts"`
ActorID string `json:"actor_id"`
ActorType string `json:"actor_type"`
}
type Users struct {
ID string `json:"id"`
}
type Text struct {
Content string `json:"content,omitempty"`
}
type MessageParts struct {
Text *Text `json:"text,omitempty"`
Image *Image `json:"image,omitempty"`
}
type Image struct {
URL string `json:"url,omitempty"`
}
func main() {
payload := &messagePayload{
Messages: []Messages{
{
MessageParts: []MessageParts{
},
ActorID: "id",
ActorType: "agent",
}},
ChannelID: "cid",
Users: []Users{
{
ID: "user1",
},
},
}
var text= new(MessageParts)
text.Text = &Text{Content: "LOL"}
var image = new(MessageParts)
image.Image= &Image{URL: "https://"}
payload.Messages[0].MessageParts = append(payload.Messages[0].MessageParts, *text)
payload.Messages[0].MessageParts = append(payload.Messages[0].MessageParts, *image)
m, err := json.Marshal(payload)
if err != nil {
fmt.Println("Error, ", err)
return
}
fmt.Println(string(m))
}