Error: the entity type requires a primary key

Question

I would like to expand the question asked on this thread

Binding listbox to observablecollection

by giving it an ability to persistent the data. The structur

Answer 1

The entity type 'DisplayFormatAttribute' requires a primary key to be defined.

In my case I figured out the problem was that I used properties like this:

public string LastName { get; set; }  //OK
public string Address { get; set; }   //OK 
public string State { get; set; }     //OK
public int? Zip { get; set; }         //OK
public EmailAddressAttribute Email { get; set; } // NOT OK
public PhoneAttribute PhoneNumber { get; set; }  // NOT OK

Not sure if there is a better way to solve it but I changed the Email and PhoneNumber attribute to a string. Problem solved.