Update related entities Entity Framework DbContext

I'm using EF with a DbContext and several POCO entities

     public class Customer
    {
        public int ID { get; set; }

        public string CompanyName { get; set; }

        public string Address { get; set; }

        public string Email { get; set; }

        public string Phone { get; set; }

        public List<Project> Projects { get; set; }

        public List<ContactPerson> ContactPersons { get; set; }
}

    public class ContactPerson
        {
            public int ID { get; set; }

            public string Name { get; set; }

            public string Email { get; set; }

            public string Phone { get; set; }
}



public class Quotation
    {
        public int ID { get; set; }

        public string QuotationName { get; set; }

        public DateTime DateCreated { get; set; }

        public ContactPerson ContactPersonAssigned { get; set; }

        public string OurReference { get; set; }

        public string QuotationDataString { get; set; }
}

Now, I need to update a quotation

        using (var myDB = new MyDB())
        {   
            Quotation quotationDB = myDB.Quotations.Find(this.quotation.ID);
            quotationDB.QuotationName = textBox_name.Text;
            quotationDB.OurReference = textBox_quotedBy.Text;
            quotationDB.ContactPersonAssigned = null;
            quotationDB.ContactPerson开发者_开发技巧Assigned = myDB.ContactPersons.Find(((ContactPerson)this.comboBox_YourReference.SelectedItem).ID);
            quotationDB.DateCreated = this.dateTimePicker_dateQuoted.Value;

 myDB.SaveChanges();
                }

All the fields in quotationDB will update, except for quotationDB.ContactPersonAssigned which will never be updated. Why? The actual object updates correctly, but no changes are save into the database.

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you need to define navigation properties as virtual

 public virtual ContactPerson ContactPersonAssigned { get; set; }