EntityDataModel set parent key to null on insert or update

I am working in asp.net 3.5 sp1. I have two tables

User
  UserID PK (int)
  UserName (varchar)
  ContactInfoID FK (int) Allow Null

ContactInfo
  ConactInfoID PK (int)
  Address (varchar)
  City (varchar)
  State (varchar)
  Zip (varchar)

I am trying to use EDM to insert/update a user with no corresponding parent ContactInfo. The database allows for this.

I want to be able to set the ContactInfo_ContactInfoI开发者_C百科D = -1 to represent a null parent. I have the following function in the User partial class. I included the errors I am getting when I tried setting different aspects of the EntityKey to null.

        public int ContactInfo_ContactInfoID
        {
            get
            {
                if (this.ContactInfoReference == null)
                    return -1;

                if (this.ContactInfoReference.EntityKey == null)
                    return -1;

                return (int)this.ContactInfoReference.EntityKey.EntityKeyValues [0].Value;
            }
            set
            {
                //To notify others listening that the property is changing
                this.OnPropertyChanging ("ContactInfoReference_ContactInfoD");

                if (value != -1)
                {
                    //Always needs to create a new EntityKey object
                    this.ContactInfoReference.EntityKey =
                        new EntityKey (
                            "ProjectRedEntities.ContactInfo",
                            new EntityKeyMember []
                                { new EntityKeyMember("ContactInfoID",
                                    (object)value) });
                }
                else
                {
//                    this.ContactInfoReference.EntityKey = null;
                    // ERROR: A relationship is being added or deleted from an AssociationSet 'FK_User_ContactInfo'. With cardinality constraints, a corresponding 'User' must also be added or deleted.

//                    this.ContactInfoReference.Value = null;
                    // ERROR : A relationship is being added or deleted from an AssociationSet 'FK_User_ContactInfo'. With cardinality constraints, a corresponding 'User' must also be added or deleted.
//                    this.ContactInfoReference.EntityKey =
//                        new EntityKey (
//                            "ProjectRedEntities.ContactInfo", "ContactInfoID", null);
                    // ERROR: Value cannot be null.

//                    this.ContactInfoReference.EntityKey = EntityKey.NoEntitySetKey;
                    // ERROR: The EntityKey property cannot be set to EntityNotValidKey, NoEntitySetKey, or a temporary key.

//                    this.ContactInfoReference.EntityKey =
//                        new EntityKey ();
                    // ERROR The EntityKey property cannot be set to EntityNotValidKey, NoEntitySetKey, or a temporary key.
                }
                //To notify others listenging that the property has changed
                this.OnPropertyChanged ("ContactInfoReference_ContactInfoID");
            }
        }

If I try to set the nullable field in the relationship to true then I get a compile error

'ContactInfoID' for type ContactInfo is not valid. All parts of the key must be non nullable.

I can load a User from the database which has a null ContactInfoID, but anytime I try to set the EntityKey to null I get exceptions.

How do I set the User.ContactInfoID to null?

User.ContactID cannot be set to -1 to represent a missing value; rather than mucking with the entitykey, can't you use null to do this? EF wasn't built to use -1 as that designation...