Select thymeleaf doesn't create a value in my db - spring

Question

I have a project of library in spring with thymeleaf and MySQL. I have a form of book in which I have select option with author and other with editorial. I receive a list of all of them from my ddbb, but when I submit in the button the data doesn't create a registry in my ddbb, But when I use input its work fine.
here is the code
HTML
<div class="form-group">
<label class="col-sm-2 col-form-label">Autor</label>
<div class="col-sm-6">
<select th:field="*{autor}" id="provincia">
<option th:each="autor:${autores}" th:text="${autor.nombre}"
th:value="${autor.id}" />
</select>
<!-- <input type="text" th:field="*{autor.id}" class="form-control" th:errorclass="'form-control alert-danger'" />-->
<!-- <small class="form-text text-danger" th:if="${#fields.hasErrors('autor.id')}" th:errors="*{autor.id}"></small> -->
</div>
</div>
<div class="form-group">
<label class="col-sm-2 col-form-label">Editorial</label>
<div class="col-sm-6">
<select th:field="*{editorial}">
<option th:each="editorial:${editoriales}"
th:text="${editorial.nombre}" th:value="${editorial.id}" />
</select>
<!-- <input type="text" th:field="*{editorial.id}" class="form-control" th:errorclass="'form-control alert-danger'" />-->
<!-- <small class="form-text text-danger" th:if="${#fields.hasErrors('editorial.id')}" th:errors="*{editorial.id}"></small> -->
</div>
</div>
Here is the controller
#RequestMapping(value = "/form_lib")
public String crearLibro(Model model) {
Libro libro = new Libro();
model.addAttribute("libro", libro);
model.addAttribute("titulo", "Formulario crear Libro");
model.addAttribute("autores", autorDao.listaAutores());
model.addAttribute("editoriales", editorialDao.listaEditoriales());
return "form_lib";
}
#RequestMapping(value = "/form_lib", method = RequestMethod.POST)
public String guardarLibro(#Valid #ModelAttribute Libro libro, BindingResult result, Model model,
#RequestParam("file") MultipartFile imagen, RedirectAttributes attributes) {
if (result.hasErrors()) {
model.addAttribute("titulo", "Formulario de Libro");
model.addAttribute("libro", libro);
System.out.println("errrorrrr");
return "listar_libro";
}
if (!imagen.isEmpty()) {
=Paths.get("src//main//resources//static/images");
String rutaAbsoluta = "//home//marce//Documentos//imagen";
try {
byte[] bytesImg = imagen.getBytes();
Path rutaCompleta = Paths.get(rutaAbsoluta + "//" + imagen.getOriginalFilename());
Files.write(rutaCompleta, bytesImg);
libro.setImagen(imagen.getOriginalFilename());
} catch (IOException e) {
e.printStackTrace();
}
}
System.out.println(libro.toString());
libroDao.guardarLibro(libro);
return "redirect:/form_lib";
}
Here is the entity
#Entity
#Table(name = "libros")
public class Libro implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id_libro")
private int id;
#Column(name = "isbn")
private long isbn;
#Column(name = "titulo")
private String titulo;
#Column(name = "anio")
private int anio;
#Column(name = "ejemplares")
private int ejemplares;
#Column(name = "ejemplaresp")
private int ejemplaresPrestados;
#Column(name = "ejemplaresr")
private int ejemplaresRestantes;
#Column(name = "alta")
private boolean alta;
#Column(name = "imagen")
private String imagen;
#OneToOne
#JoinColumn(name="id_autor")
private Autor autor;
#OneToOne
#JoinColumn(name="id_editorial")
private Editorial editorial;