public class Book
{
    [Key]
    public int Id { get; set; }

    [Required]
    [Display(Name = "Tytuł")]

    public string Title { get; set; }
    [Required]
    [Display(Name = "Autor")]
    public string Author { get; set; }
    [Required]
    [Display(Name = "Gatunek")]
    public string Genre { get; set; }
    [Required]
    [Display(Name = "Rok Wydania")]
    public int ReleaseYear { get; set; }
    [Required]
    [Display(Name = "Okładka")]
    public string Cover { get; set; }
    [Required]
    [Display(Name = "Liczba Stron")]
    public int NumberOfPages { get; set; }
    [Required]
    [Display(Name = "Opis")]
    public string Description { get; set; }
}

[Key]
    public int Id { get; set; }

    [Required]
    [Display(Name = "Gatunek")]
    public string Name { get; set; }

public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {

    }

    public DbSet<Book> Book { get; set; }
    public DbSet<Genre> Genre { get; set; }

[Authorize(Roles = SD.AdminEndUser)]
public class AddBookModel : PageModel
{
    private readonly ApplicationDbContext _db;

    [BindProperty]
    public Book Book { get; set; }

    public AddBookModel(ApplicationDbContext db)
    {
        _db = db;
    }

    public IActionResult OnGet()
    {
        return Page();
    }

    public async Task <IActionResult> OnPostAsync(ServiceType ServiceType)
    {
        if(!ModelState.IsValid)
        {
            return Page();
        }

        _db.Book.Add(Book);
        await _db.SaveChangesAsync();

        return RedirectToPage("Index");

    }

<form method="post">
<div class="border backgroundWhite">
    <div class="form-group row">
        <div class="col-2">
            <label asp-for="Book.Title"></label>
        </div>
        <div class="col-5">
            <input asp-for="Book.Title" class="form-control" />
        </div>
        <span asp-validation-for="Book.Title" class="text-danger"></span>
    </div>
    <div class="form-group row">
        <div class="col-2">
            <label asp-for="Book.Author"></label>
        </div>
        <div class="col-5">
            <input asp-for="Book.Author" class="form-control" />
        </div>
        <span asp-validation-for="Book.Author" class="text-danger"></span>
    </div>
    <div class="form-group row">
        <div class="col-2">
            <label asp-for="Book.Genre"></label>
        </div>
        <div class="col-5">
            <input asp-for="Book.Genre" class="form-control" />
        </div>
        <span asp-validation-for="Book.Genre" class="text-danger"></span>
    </div>
    <div class="form-group row">
        <div class="col-2">
            <label asp-for="Book.ReleaseYear"></label>
        </div>
        <div class="col-5">
            <input asp-for="Book.ReleaseYear" class="form-control" />
        </div>
        <span asp-validation-for="Book.ReleaseYear" class="text-danger"></span>
    </div>
    <div class="form-group row">
        <div class="col-2">
            <label asp-for="Book.NumberOfPages"></label>
        </div>
        <div class="col-5">
            <input asp-for="Book.NumberOfPages" class="form-control" />
        </div>
        <span asp-validation-for="Book.NumberOfPages" class="text-danger"></span>
    </div>
    <div class="form-group row">
        <div class="col-2">
            <label asp-for="Book.Cover"></label>
        </div>
        <div class="col-5">
            <input asp-for="Book.Cover" class="form-control" />
        </div>
        <span asp-validation-for="Book.Cover" class="text-danger"></span>
    </div>
    <div class="form-group row">
        <div class="col-2">
            <label asp-for="Book.Description"></label>
        </div>
        <div class="col-5">
            <input asp-for="Book.Description" class="form-control" />
        </div>
        <span asp-validation-for="Book.Description" class="text-danger"></span>
    </div>
    <div class="form-group row">
        <div class="col-5 offset-2">
           <partial name="_AddAndBackToListButton" />
        </div>
    </div>
</div>