Write to JSON failed, please help to check.

package main

import (
    "database/sql"
    "github.com/ant0ine/go-json-rest/rest"
    _ "github.com/lib/pq"
    "log"
    "net/http"
)

func main() {

    api := rest.NewApi()
    api.Use(rest.DefaultDevStack...)
    router, err := rest.MakeRouter(
        rest.Get("/books", GetAllBooks),
    )
    if err != nil {
        log.Fatal(err)
    }
    api.SetApp(router)
    log.Fatal(http.ListenAndServe(":8000", api.MakeHandler()))
}

type Book struct {
    isbn   string  `json:"isbn"`
    title  string  `json:"title"`
    author string  `json:"author"`
    price  float32 `json:"price"`
}

var db *sql.DB

func init() {
    var err error
    db, err = sql.Open("postgres", "postgres://postgres:123456@localhost/test")
    if err != nil {
        log.Fatal(err)
    }

    if err = db.Ping(); err != nil {
        log.Fatal(err)
    }
}

func GetAllBooks(w rest.ResponseWriter, r *rest.Request) {
    rows, err := db.Query("SELECT * FROM books")
    if err != nil {
        rest.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    defer rows.Close()
    books := make([]Book, 10)
    for rows.Next() {
        var book Book
        err := rows.Scan(&book.isbn, &book.title, &book.author, &book.price)
        if err != nil {
            rest.Error(w, err.Error(), http.StatusInternalServerError)
            return
        }
        books = append(books, book)
    }
    if err = rows.Err(); err != nil {
        rest.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    w.WriteJson(books)
}

Output:
[
{},
{},
{},
{},
{},
{},
{},
{},
{},
{},
{},
{},
{},
{},
{}
]

Database table records:

      isbn      |      title       |       author        | price
----------------+------------------+---------------------+-------
 978-1503261969 | Emma             | Jayne Austen        |  9.44
 978-1505255607 | The Time Machine | H. G. Wells         |  5.99
 978-1503379640 | The Prince       | Niccolò Machiavelli |  6.99
 978-1470184842 | Metamorphosis    | Franz Kafka         |  5.90
(4 rows)

Question: Not sure why the output is always empty, someone could help?

---

The json package only accesses the exported fields of struct types (those that begin with an uppercase letter). Therefore only the the exported fields of a struct will be present in the JSON output.