Entity framework - Define connection where neither side is required - asp.net-mvc

Question

I have a problem, I have to create a model where we have two entities which CAN be linked together but can also exist as stand alone entities.
The model currently looks like this:
public class Authorisation
{
public int AuthorisationID { get; set; }
public virtual Change Change { get; set; }
}
public class Change
{
public int ChangeID{ get; set; }
public virtual Authorisation Authorisation { get; set; }
public int? AuthorisationID{ get; set; }
}
The reason for this is that we can have an authorization record independent of a change, and some changes require authorisation and some dont, so neither side of the relationship is required.
I can configure this with the fluent API like so:
modelBuilder.Entity<Authorisation>()
.HasOptional(t => t.Change)
.WithOptionalPrincipal(t => t.Authorisation);
And alls well, Except that the migration that it creates looks like this
CreateTable(
"dbo.Changes",
c => new
{
ChangeID = c.Int(nullable: false, identity: true),
AuthorisationID = c.Int(),
Authorisation_AuthorisationID = c.Int(),
})
.PrimaryKey(t => t.ChangeID)
.ForeignKey("dbo.Authorisations", t => t.Authorisation_AuthorisationID)
.Index(t => t.Authorisation_AuthorisationID);
EF is deciding that its going to add a new column (Authorisation_AuthorisationID) for me to use as the FK between the two entities, what I really want to be able to do is to use the change.AuthorisationID property as the FK onto the Authorisation, I cannot find a way to configure this at all (Please note that I need the FK to be in the model - for consistency with the rest of the app more than anything else).
To sum up I need to be able to create a relationship between two entities where both sides of the relationship are optional and if possible I want to be able to define the FK column myself.
Am I just approaching this wrong? Ive been staring at the same block of code for so long I could be missing something simple.

Answer 1

Looks like explicit foreign key property is not supported for one-to-one relationships - there is no HasForeignKey Fluent API and also if you put ForeignKey attribute on the navigation property you get exception saying that multiplicity must be *.
So the only choice you have is to remove the explicit Change.AuthorisationID property and work only with navigation properties:
Model:
public class Authorisation
{
public int AuthorisationID { get; set; }
public virtual Change Change { get; set; }
}
public class Change
{
public int ChangeID{ get; set; }
public virtual Authorisation Authorisation { get; set; }
}
Configuration:
modelBuilder.Entity<Authorisation>()
.HasOptional(t => t.Change)
.WithOptionalPrincipal(t => t.Authorisation)
.Map(a => a.MapKey("AuthorisationID"));