如何使用mgo插入文档并获取返回值

For the record, I'm learning Go. I'm trying to use and the mgo package and I'd like to insert a new document and return this newly created document to user (I'm trying to write a basic API). I've wrote the following code:

EDIT: Here's the struct for the model:

type Book struct {
  ISBN    string   `json:"isbn"`
  Title   string   `json:"title"`
  Authors []string `json:"authors"`
  Price   string   `json:"price"`
}

session := s.Copy()
defer session.Close()

var book Book
decoder := json.NewDecoder(r.Body)
err := decoder.Decode(&book)
if err != nil {
    ErrorWithJSON(w, "Incorrect body", http.StatusBadRequest)
    return
}

c := session.DB("store").C("books")

info, err := c.Upsert(nil, book)

if err != nil {
    ErrorWithJSON(w, "Database error", http.StatusInternalServerError)
log.Println("Failed insert book: ", err)
    return
}

respBody, err := json.MarshalIndent(info, "", "  ")
if err != nil {
    log.Fatal(err)
}

ResponseWithJSON(w, respBody, http.StatusOK)

Please note that Book is a struct I have created earlier. The above code does work but what it returns is the upsert result like so:

{
    "Updated": 1,
    "Removed": 0,
    "Matched": 1,
    "UpsertedId": null
}

Which is not the recently created object. How can I get the the recently created object to return as a response (please note that ideally I'd like the confirmation that the document was successfully inserted. I have seen other questions where the ID is generated beforehand but for what I've seen it doesn't confirm that the document was created was it?)