EF 4.1 one to one Mapping

I have two tables Employees and Positions.

Employee

EmployeeId (PK)

PositionId (FK, Nullable)

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Position

PositionId (PK)

A position can be created and not be assigned. However, an active employee requires a position. A position can only be assigned to one employee. We enforce this by having a Unique Constraint on Employee.PositionId.

In my models, I want to have an Employee property in Position and I am having issues mapping this.

I've tried

modelBuilder.Entity<Employee>().HasRequired(e => e.Position)
                               .WithOptional(p => p.Employee);

However this ends up mapping the Employee.EmployeeId to Position.PositionId column, instead of Employee.PositionId to Position.PositionId (at least from what I can tell...)

Is my only option to make map this as a One to Many relationship even though I am forcing 1-1 through unique constraint?

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Quoting from: http://weblogs.asp.net/manavi/archive/2011/01/23/associations-in-ef-code-first-ctp5-part-3-one-to-one-foreign-key-associations.aspx

Code First (and EF in general) does not natively support one-to-one foreign key associations. In fact, EF does not support any association scenario that involves unique constraints at all.

In fluent api:

modelBuilder.Entity<Employee>()
            .HasRequired(e => e.Position)
            .WithMany()
            .HasForeignKey(e => e.PositionId);

Then override the Seed method:

protected override void Seed(EntityMappingContext context)
{
context.Database.SqlCommand("ALTER TABLE Employees ADD CONSTRAINT uc_Position UNIQUE(PositionId)");
}