Is it possible to have a struct with multiple JSON tags?

Question

I post a request to a server and get a reply in JSON format. I'm able to unmarshal it to a struct. Then I need to create a new JSON file with the same data but different JSON tags.

Example:

In the following code, I get {"name":"Sam","age":20} from a server and unmarshal it to the struct Foo:

type Foo struct {
    Name string `json:"name"`
    Age  int    `json:"age"`
}

Then I need to change the tag name to employee_name and omit age:

type Bar struct {
    Name string `json:"employee_name"`
    Age  int    `json:"-"`
}

After that I send this modified data to another server.

I know I could just create a new Bar and copy all data into it, but there are a lot of fields. I was wondering if there is a way to attach multiple JSON tags like this:

type Foo struct {
    Name string `json:"name" json:"employee_name"`
    Age  int    `json:"age" json:"-"`
}        

Thanks in advance.

Answer 1

It's not possible. The encoding/json package only handles the json key in struct tags. If the json key is listed multiple times (as in your example), the first occurrence will be used (this is implemented in StructTag.Get()).

Note that this is an implementation restriction of the encoding/json package and not that of Go. One could easily create a similar JSON encoding package supporting either multiple tag keys (e.g. json1, json2) or multiple occurrences of the same key (as in your example).