Primary /Foreign Key in Entity Framework

I think by “not using EF ORM designer” you mean new DbContext API from EF 4.1. Because if you don’t mean DbContext API you still have to use EDMX (designer).

You can either use data annotations (System.ComponentModel.DataAnnotations): KeyAttribute and ForeignKeyAttribute:

public class Registry
{
    public virtual int Id { get; set; }
    public virtual MyEntity MyEntity { get; set; }
}

public class MyEntity
{
    [Key, ForeignKey("Registry")]
    public virtual int RegistryId { get; set; }

    public virtual Registry Registry { get; set; }
}

Or you can use fluent API (overriding OnModelCreating in your derived context):

(Edit: fluent mapping was reversed and incomplete)

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    modelBuilder.Entity<MyEntity>()
                .HasKey(e => e.RegistryId);
    modelBuilder.Entity<MyEntity>()
                .Property(e => e.RegistryId)
                .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);
    modelBuilder.Entity<MyEntity>()
                .HasRequired(e => e.Registry)
                .WithRequiredDependent(r => r.MyEntity);
}

Where MyEntity is your entity with FK and Registry is principal entity in 1:1 relationship.