EF code first - one-to-one-or-zero - entity-framework

Question

I have 2 entities:
public partial class GPSdevice
{
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
public GPSdevice()
{
}
public int ID { get; set; }
public string UserName { get; set; }
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
public virtual Truck Truck { get; set; }
}
public partial class Truck
{
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
public Truck()
{
}
public int TruckID { get; set; }
public string TruckNo { get; set; }
public string Make { get; set; }
[ForeignKey("GPSdevice")]
public int? GPSdeviceID { get; set; }
public virtual GPSdevice GPSdevice { get; set; }
}
I want to create a relationship one-to-one-or-zero (each GPSdevice can be linked to any truck (but to one and only one) or not linked at all)
I write the following code:
modelBuilder.Entity<GPSdevice>()
.HasOptional(e => e.Truck)
.WithOptionalPrincipal()
.WillCascadeOnDelete(false);
but it creates the following migration:
public override void Up()
{
AddColumn("dbo.Truck", "GPSdevice_ID", c => c.Int());
CreateIndex("dbo.Truck", "GPSdeviceID");
CreateIndex("dbo.Truck", "GPSdevice_ID");
AddForeignKey("dbo.Truck", "GPSdeviceID", "dbo.GPSdevices", "ID");
AddForeignKey("dbo.Truck", "GPSdevice_ID", "dbo.GPSdevices", "ID");
}
why it creates one more field and how to use the current field GPSdeviceID instead?
ADDED:
If I remove
public int? GPSdeviceID { get; set; }
and add MapKey:
modelBuilder.Entity<GPSdevice>()
.HasOptional(e => e.Truck)
.WithOptionalPrincipal(e=>e.GPSdevice).Map(p=>p.MapKey("GPSdeviceID"))
.WillCascadeOnDelete(false);
in result I get the following migration code:
public override void Up()
{
CreateIndex("dbo.Truck", "GPSdeviceID");
AddForeignKey("dbo.Truck", "GPSdeviceID", "dbo.GPSdevices", "ID");
}
then I get the following error:
There are no primary or candidate keys in the referenced table
'dbo.GPSdevices' that match the referencing column list in the foreign
key 'FK_dbo.Truck_dbo.GPSdevices_GPSdeviceID'. Could not create
constraint or index. See previous errors.

Answer 1

Use this :
public partial class GPSdevice
{
public GPSdevice()
{
}
public int ID { get; set; }
public string UserName { get; set; }
public virtual Truck Truck { get; set; }
}
public partial class Truck
{
public Truck()
{
}
public int TruckID { get; set; }
public string TruckNo { get; set; }
public string Make { get; set; }
public virtual GPSdevice GPSdevice { get; set; }
}
modelBuilder.Entity<GPSdevice>()
.HasOptional(o => o.Truck)
.WithRequired(ad => ad.GPSdevice);
modelBuilder.Entity<Truck>()
.HasKey(e => e.TruckID);