Question

I’m having a problem loading entities from an EF 4.3 Code First database.
I’ve simplified my code down to this working sample code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Entity;
using System.ComponentModel.DataAnnotations;
using System.Data.Entity.Infrastructure;

namespace CodeFirst {
    class Program {
        static void Main(string[] args) {
            Database.SetInitializer(new DropCreateDatabaseAlways<Context>());
            Database.DefaultConnectionFactory = new SqlCeConnectionFactory("System.Data.SqlServerCe.4.0");

            using (Context context = new Context()) { 
                A a = new A { B = new B { Foo = 1 } };
                context.As.Add(a);
                context.SaveChanges();
                Print(context); // B has ID=1, Foo=1
            }

            using (Context context = new Context()) { 
                Print(context); // B is null
            }

            Console.ReadLine();
        }

        public static void Print(Context context) {
            A a = context.As.Single();
            Console.WriteLine("A: ID=" + a.Id);
            if (a.B == null) {
                Console.WriteLine("B: null");
            }
            else { 
                Console.WriteLine("B: ID=" + a.B.Id + ", Foo=" + a.B.Foo);
            }
        }
    }

    class Context : DbContext {
        public DbSet<A> As { get; set; }
    }

    class A {
        public int Id { get; set; }
        public B B { get; set; }
    }

    class B {
        public int Id { get; set; }
        public int Foo { get; set; }
    }
}

The output is:

A: ID=1
B: ID=1, Foo=1
A: ID=1
B: null

In this sample code, for some reason when I retrieve A in a new Context, its subproperty B is null. If I set a breakpoint and connect to the database at the point where B is null, everything looks to be in order:

Table: A
--------
Id    B_Id
1     1

Table: B
--------
Id    Foo
1     1

I’m just trying to learn Code First, so I may have a gross misunderstanding here, but this seems very strange to me. Can anyone explain this behavior?

Answer 1

Both answers provided so far are unnecessarily cumbersome.

Just make your entity classes public and declare your navigation properties as virtual, and EF will load them lazily (i.e. on demand)

The DbContext must be open (i.e. not disposed) when you access the navigation property for this to work.