Dynamic JSON struct in Golang doesn't behave as expected - json

Question

I'm trying to create a struct with some basic fields which are always present and some optional fields which are structs by themselves.
I'm wondering why the following code:
package main
import (
"encoding/json"
"fmt"
"time"
)
type DataManagement struct {
DataManagement struct {
Type string
Asset struct {
LocalAssetUID string
Type string
}
*ContentProductionOrder
*ContentItem
TimeStamp time.Time
Hash string
}
}
type ContentProductionOrder struct {
ProductionOrderNo int
ItemNo int
StartDate time.Time
FinishDate time.Time
StatusID int
StatusDate time.Time
SourceTypeID int
TrackingID int
}
type ContentItem struct {
ItemNo int
ItemText string
Quantity int
}
func main() {
var contentItem ContentItem
contentItem.ItemNo = 123
contentItem.ItemText = "aaaaaaaa"
contentItem.Quantity = 3
var dataManagement DataManagement
dataManagement.DataManagement.Type = "asd"
dataManagement.DataManagement.Asset.LocalAssetUID = "asd"
dataManagement.DataManagement.Asset.Type = "asd"
dataManagement.DataManagement.ContentItem = &contentItem
dataManagement.DataManagement.TimeStamp = time.Now().UTC()
dataManagement.DataManagement.Hash = "123"
xy, _ := json.MarshalIndent(dataManagement, "", " ")
fmt.Println(string(xy))
xy, _ = json.MarshalIndent(contentItem, "", " ")
fmt.Println(string(xy))
}
outputs to the following:
{
"DataManagement": {
"Type": "asd",
"Asset": {
"LocalAssetUID": "asd",
"Type": "asd"
},
"ItemText": "aaaaaaaa",
"Quantity": 3,
"TimeStamp": "2009-11-10T23:00:00Z",
"Hash": "123"
}
}
{
"ItemNo": 123,
"ItemText": "aaaaaaaa",
"Quantity": 3
}
and not to:
{
"DataManagement": {
"Type": "asd",
"Asset": {
"LocalAssetUID": "asd",
"Type": "asd"
},
"ContentItem": {
"ItemNo": 123,
"ItemText": "aaaaaaaa",
"Quantity": 3
},
"TimeStamp": "2009-11-10T23:00:00Z",
"Hash": "123"
}
}
{
"ItemNo": 123,
"ItemText": "aaaaaaaa",
"Quantity": 3
}
Any ideas? It's probably pretty easy to explain; I'm not that experienced in Golang.
Here's a Playground link: https://play.golang.org/p/iRDcaRIZ_ZU

Answer 1

The output you are not getting which you want is because you have used embedded struct for ContentItem in DataManagement rather than field name to add to the struct.
A field declared with a type but no explicit field name is called an
embedded field. An embedded field must be specified as a type name T
or as a pointer to a non-interface type name *T, and T itself may not
be a pointer type. The unqualified type name acts as the field name.
A field declaration will sove your issue. You should change the struct DataManagement to:
type DataManagement struct {
DataManagement struct {
Type string
Asset struct {
LocalAssetUID string
Type string
}
*ContentProductionOrder // this is embedded struct
ContentItem *ContentItem
TimeStamp time.Time
Hash string
}
}
Working Code on Go Playground
For more information, Have a look at Golang Spec for Struct Types