Entity framework una chiave esterna verso due tabelle: prima il codice

Tutto, è possibile utilizzare lo stesso FK per due tavoli. Probabilmente non è una buona pratica, ma ho due classi diverse che possono essere prenotate entrambe:

public class Course {

    public Course() {
        BookingRefs = new HashSet<BookingRef>();
    }

    public long Id { get; set; }
    public string Title { get; set; }
    // other props ...

    [InverseProperty(nameof(BookingRef.Course))]
    public virtual ICollection<BookingRef> BookingRefs { get; set; }
}

public class GiftCard {

    public GiftCard() {
        BookingRefs = new HashSet<BookingRef>();
    }

    public long Id { get; set; }
    public string Prop1 { get; set; }
    public int Prop2 { get; set; }
    // other props ...

    [InverseProperty(nameof(BookingRef.Course))]
    public virtual ICollection<BookingRef> BookingRefs { get; set; }
}

// this is the bookin reference for a Course or an GiftCard
public class BookingRef {

    public BookingRef() {
    }

    public long Id { get; set; }
    // other props ...

    /// <summary>The item (usually the course but theoretically anything with a long id)</summary>
    public long? ItemId { get; set; }

    // maybe a generic Object?
    [ForeignKey(nameof(ItemId))]
    public Object GiftCard { get; set; }

    // maybe 2 items possibly null?
    [ForeignKey(nameof(ItemId))]
    public Course Course { get; set; }

    // maybe 2 items possibly null?
    [ForeignKey(nameof(ItemId))]
    public GiftCard GiftCard { get; set; }
}