Append value to c.Json response - go

Question

I want to append a value to the returned response of my code, this is what I already have:
publisherShare := 25 // I also have this variable that want to append to the returned response.
c.JSON(http.StatusOK, nf) // nf is a row found and returned from database.
This returns such json:
{
"id": 105324,
"title": "test title",
"last_update": "2021-03-10T12:50:37+03:30",
"created_at": "2021-03-10T12:50:36+03:30",
"updated_at": "2021-05-05T05:46:39.352859604Z"
}
I need to have a json result like this:
{
"id": 105324,
"title": "test title",
"last_update": "2021-03-10T12:50:37+03:30",
"created_at": "2021-03-10T12:50:36+03:30",
"updated_at": "2021-05-05T05:46:39.352859604Z",
"publisher_share": 25 // I want this to be added.
}
This is what I have tried so far, but it changes the schema and will not be backward compatible anymore:
c.Json(http.StatusOK, gin.H{"book": nf, "publisher_share": publisherShare})
but this is not the json result I want. I want publisher_share alongside other fields just like the json result I mentioned above.

Answer 1

You can add publisher share to the same type as
type nfType struct {
// All of the db row fields
PublisherShare int `json:"publisher_share,omitempty" db:"-"`
}

Answer 2

Simply create a struct that matches the structure of your json responce. Key is to add aditional fild to it like
type Responce struct {
// other fields. They have to be written in same way to keep conventions
// (Go-ish name and needed name as tag)
PublisherShare int `json:"publisher_share"`
}
Then when you handle responce you can just unmarshal and marshal json.
responce := Responce{PublisherShare: 25}
err := json.Unmarshal(bytes, &responce)
if err != nil {
//handle error
}
newResponce, err := jsom.Marshal(responce)
if err != nil {
//handle error
}
// newResponce is now in form you want

Answer 3

Define a new type. It embeds the type of the db row, and it has a field for the extra value. E.G: if the type of the db row is DatabaseRow:
type CompleteReturn struct {
DatabaseRow
PublisherShare int `json:"publisher_share"`
}
Later use it as:
complete := CompleteReturn{
DatabaseRow: nf, // Serialize in json as before
PublisherShare: 25, // Serialize in json as publisher_share
}
c.Json(http.StatusOk, complete)