ASP.NET C# EF Core migration error

Question

When I run a migration I get the following error:

The given key 'System.Nullable1[System.Int32] ChildId' was not present in the dictionary.

Basically I want to create a relationship for a contact with another contact, e.g. Contact1 has a relationship with Contact2 of type Employee. One Contact can have many relationships with other Contacts. There is only one relationship type for each relationship. So under Contact1 you may see 3 relationship recrods, e.g.  Contact2;Supervisor, Contact2;Friend, Contact3; Dentist.

My navigation properties are wrong, but I can't figure out how to set this up. Any help would be greatly appreciated :)

Contact Model

public class Contact
    {
        public int Id { get; set; }
        public string? FirstName { get; set; }
        public string? LastName { get; set; }

        [InverseProperty(nameof(Relationship.ParentId))]
        public virtual ICollection<Relationship> Parent { get; set; }

        [InverseProperty(nameof(Relationship.ChildId))]
        public virtual ICollection<Relationship> Child { get; set; }
    }

 

Relationship Model

public class Relationship
    {
        public int Id { get; set; }

        [ForeignKey(nameof(Parent)), Column(Order = 0)]
        public int? ParentId { get; set; }
        public virtual Contact? Parent { get; set; }

        [ForeignKey(nameof(Child)), Column(Order = 1)]
        public int? ChildId { get; set; }
        public virtual Contact? Child { get; set; }

        // Navigation for the relationship type
        public int? RelationshipId { get; set; }
        public virtual Relationship? Relationships { get; set; }
    }