EntityFramework Object Not Set to Instance of Object in Model Creation

Question

I have been struggling for a while now to convert a fairly large EntityFramework database created in model first to codefirst. I have a problem that I cant seem to resolve. I am getting an Object reference not set to an instance of an object with the following procedures on the call stack.

ModelConfiguration.Configuration.Types.EntityTypeConfiguration.Configure
ModelConfiguration.Configuration.ModelConfiguration.ConfigureEntities

to simplify the post I have created a test project that boils the problem down to its simplest form.

I have 3 classes

a which has an has an optional b and an optional c
b which has a collection of a's, and a colleciton of c's

c which has an optional b and a collection of a's

public class a
{
    public int Id { get; set; }
    [Required]
    public string name { get; set; }

    public virtual b b { get; set; }
    [ForeignKey("b")]
    public int? b_Id { get; set; }

    public virtual c c { get; set; }
    [ForeignKey("c")]
    public int? c_Id { get; set; }
}

public class b
{
    public int Id { get; set; }
    public string name { get; set; }

    public virtual ICollection<a> a_s { get; set; }
    public virtual ICollection<c> c_s { get; set; }
}

public class c
{
    public int Id { get; set; }

    public virtual b b { get; set; }
    [ForeignKey("b")]
    public int? b_Id { get; set; }

    public virtual ICollection<a> a_s { get; set; }
}

public class MyContext : DbContext
{
    public DbSet<a> a { get; set; }
    public DbSet<b> b { get; set; }
    public DbSet<c> c { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<a>()
            .HasOptional(m => m.b)
            .WithMany(m => m.a_s);

        modelBuilder.Entity<b>()
            .HasMany(m => m.c_s)
            .WithRequired(m => m.b);

        modelBuilder.Entity<c>()
            .HasMany(m => m.a_s)
            .WithOptional(m => m.c);

        base.OnModelCreating(modelBuilder);
    }

}

when I execute the code var a = from o in db.a select o, I get the error described above. There is absolutely no information on what is hapenning, so I really dont know where to turn. Can anyone help me solve this problem, as I really want to move away from Model First.

namespace MvcApplication2.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            var db = new MyContext();

            var a = from o in db.a select o;

            return View();
        }

    }
}

Eranga · Accepted Answer · 2012-03-20 01:32:25Z

3

The mixup of fluent configuration and data annotation caused this problem. EF team should have handled this exception and given a meaningful error message.

Remove data annotations and use fluent configuration as follows

public class a
{
    public int Id { get; set; }

    [Required]
    public string name { get; set; }

    public virtual b b { get; set; }

    public int? b_Id { get; set; }

    public virtual c c { get; set; }

    public int? c_Id { get; set; }
}

public class b
{
    public int Id { get; set; }
    public string name { get; set; }

    public virtual ICollection<a> a_s { get; set; }
    public virtual ICollection<c> c_s { get; set; }
}

public class c
{
    public int Id { get; set; }

    public virtual b b { get; set; }

    public int? b_Id { get; set; }

    public virtual ICollection<a> a_s { get; set; }
}

public class NreContext : DbContext
{
    public DbSet<a> a { get; set; }
    public DbSet<b> b { get; set; }
    public DbSet<c> c { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<a>()
            .HasOptional(m => m.b)
            .WithMany(m => m.a_s)
            .HasForeignKey(m => m.b_Id);

        modelBuilder.Entity<a>()
            .HasOptional(m => m.c)
            .WithMany(m => m.a_s)
            .HasForeignKey(m => m.c_Id);

        modelBuilder.Entity<c>()
            .HasOptional(m => m.b)
            .WithMany(m => m.c_s)
            .HasForeignKey(m => m.b_Id);

        base.OnModelCreating(modelBuilder);
    }
}

answered Mar 20, 2012 at 1:32

Eranga

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1 Comment

Kevin Over a year ago

that fixes the issue. Thanks. It seems that you should be able to mix and match annotations and fluent syntax but i guess i will switch to fluent for everthing

abatishchev · Accepted Answer · 2014-08-15 21:07:27Z

1

Try putting 'a' into local memory:

var a = from o in db.a.ToList() select o;

edited Aug 15, 2014 at 21:07

abatishchev

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answered Mar 20, 2012 at 0:36

Memet Olsen

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1 Comment

Kevin Over a year ago

That gives the same problem. The issue is in creating the model.

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