Entity Framework code first relationship using fluent API to string - entity-framework-5

Question

I have the following classses
public pratial class Address
{
public Guid AddressID{ get; set; }
public AddressType AddressType{ get; set; }
}
public partial class AddressType
{
public string TypeName{ get; set; }
}
In my derived DBContext class I have overridden OnModelCreating
protected override OnModelCreating(DBModelBuilder modelBuilder)
{
modelBuilder.Entity<Address>().HasKey( p => p.AddressID );
modelBuilder.Entity<Address>().Property ( p => p.AddressID)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
modelBuilder.Entity<Address>().HasRequired( p => p.AddressType);
modelBuilder.Entity<AddrssType>().HasKey( p => p.TypeName );
...
}
This creates fine I fill out a record in the database where
My Tables in the database end up looking like this
Addresses Table
AddressID (PK, uniqueidentified, not null)
AddressType_TypeName(FK, nvarchar(32), not null)
AddressTypes Table
TypeName (PK, uniqueidentifies, not null)
Now I put some data in the tables
AddressTypes Record
TypeName I put in Business
in the Addresses Record
AddressType_TypeName I put in Business
When I run a unit test on this I expect to get back in for my record
List<Address> addresses = context.Addresses.ToList()
Assert.AreEqual(addresses[0].AddressType.TypeName, "Business");
But this fails telling me AddressType is null
How do I set up the relationship between Address and AddressType so that I get back the AddressType that I've hooked up?

Answer 1

To load related entities you must tell it Entity Framework, either by using eager loading:
using System.Data.Entity;
//...
var addresses = context.Addresses.Include(a => a.AddressType).ToList()
...or by lazy loading which is enabled by default if you mark your navigation properties as virtual:
public virtual AddressType AddressType { get; set; }
Eager loading loads the parent and related data together in a single database roundtrip. Lazy loading needs two roundtrips, the second happens under the convers when you access the navigation property in the line addresses[0].AddressType.TypeName.
Edit
Test project to show that lazy loading in this example works (EF 5.0, .NET 4.0, SQL Server Express 2008 R2 as database). I only put virtual in front of AddressType. The rest is identical to your model:
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity;
using System.Linq;
namespace EFLazyLoading
{
public partial class Address
{
public Guid AddressID{ get; set; }
public virtual AddressType AddressType{ get; set; }
}
public partial class AddressType
{
public string TypeName{ get; set; }
}
public class MyContext : DbContext
{
public DbSet<Address> Addresses { get; set; }
public DbSet<AddressType> AddressTypes { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Address>().HasKey( p => p.AddressID );
modelBuilder.Entity<Address>().Property ( p => p.AddressID)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
modelBuilder.Entity<Address>().HasRequired( p => p.AddressType);
modelBuilder.Entity<AddressType>().HasKey( p => p.TypeName );
}
}
class Program
{
static void Main(string[] args)
{
Database.SetInitializer(new DropCreateDatabaseAlways<MyContext>());
using (var ctx = new MyContext())
{
var address = new Address
{
AddressType = new AddressType { TypeName = "Business" }
};
ctx.Addresses.Add(address);
ctx.SaveChanges();
}
using (var ctx = new MyContext())
{
List<Address> addresses = ctx.Addresses.ToList();
string typeName = addresses[0].AddressType.TypeName;
}
}
}
}
The result of typeName in the last line is as expected: