CODEWITHSUNDEEP
entity-framework-4ef-code-first
Niclas Lindqvist
Niclas Lindqvist

Reputation: 1432

How to make a nullable property in EF Codefirst?

I have two POCOs in my "Bookshelf" test application:

/// <summary>
/// Represents a book
/// </summary>
public class Book
{
    public int ID { get; set; }
    public string Title { get; set; }
    public string Author { get; set; }
    public string ISBN { get; set; }
    public virtual Loaner LoanedTo { get; set; }
}

/// <summary>
/// Represents a Loaner
/// </summary>
public class Loaner
{
    public int ID { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Book> Loans { get; set; }
}

Is there a way that my LoanedTo could be nullable? I mean a book isn't always loaned, right! I tried

public virtual Loaner? LoanedTo { get; set; }

But I get: The type 'RebtelTests.Models.Loaner' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'System.Nullable'

So I must be thinking wrong somewhere, but I can't figure it out. Probably easy squeeze for you guys.

Upvotes: 1

Views: 12019

Answers (3)

Sundara Prabu
Sundara Prabu

Reputation: 2729

If you are talking about a simple property like int, bool, or float use int?, bool?, or float?

like

 public int? ID { get; set; }
 public bool? Exists { get; set; }

Upvotes: 1

Kristof Claes
Kristof Claes

Reputation: 10941

You don't need to do anything special. Classes are always nullable.

I just tried this (with MVC3):

In my Models directory:

namespace MvcApplication2.Models
{
    public class Book
    {
        public int ID { get; set; }
        public string Title { get; set; }
        public string Author { get; set; }
        public string ISBN { get; set; }
        public virtual Loaner LoanedTo { get; set; }
    }

    public class Loaner
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public virtual ICollection<Book> Loans { get; set; }
    }

    public class BookContext : System.Data.Entity.DbContext
    {
        public System.Data.Entity.DbSet<Book> Books { get; set; }
        public System.Data.Entity.DbSet<Loaner> Loaners { get; set; }
    }
}

In my HomeController:

namespace MvcApplication2.Controllers
{
    public class HomeController : Controller
    {
        //
        // GET: /Home/

        public ActionResult Index()
        {
            string message = "OK";

            try
            {
                var context = new Models.BookContext();
                var book = new Models.Book();
                book.Title = "New Title";
                book.Author = "New Author";
                book.ISBN = "New ISBN";
                context.Books.Add(book);
                context.SaveChanges();
            }
            catch (Exception err)
            {
                message = err.ToString();
            }

            ViewBag.Message = message;

            return View();
        }

    }
}

The connectionstring in Web.Config:

<add name="BookContext" connectionString="Data Source=|DataDirectory|BookContext.sdf" providerName="System.Data.SqlServerCe.4.0" />

When I run the application, the view displays "OK". This means that no exception was thrown. When I look in my App_Data folder, a BookContext.sdf file has been created. That database contains a table for the Books and the Loaners. The table for the Loaners is empty. The one for the Books contains one record:

ID: 1; Title: "New Title"; Author: "New Author"; ISBN: "New ISBN"; LoanerID: null

Upvotes: 6

PsychoCoder
PsychoCoder

Reputation: 10765

Couldn't you just use something like this

public virtual Nullable<Loaner> LoanedTo { get; set; }

That then should make LoanedTo a nullable property

Upvotes: -1

Related Questions