/// <summary>
 /// Implementation of IPhoneBookRepository.AddContact(contact) which adds contact to database
 /// </summary>
 /// <param name="contact">Contact object to be added</param>
 /// <returns>Unique contact identifier</returns>
 public int AddContact(Contact contact)
 {
     if (contact == null || contact.Id != 0 || !IsContactConsistent(contact)) return 0;
     using (var db = GetPhoneBookContextInstance())
     {
         contact.Owner = Owner;
         var contactRecord = new ContactRecord(contact);
         db.Contacts.Add(contactRecord);
         db.SaveChanges();
         contact.Id = contactRecord.Id;
         return contact.Id;
     }
 }
 /// <summary>
 /// Method checks if repository user is authorized to access ContactRecord retrieved from database
 /// </summary>
 /// <param name="contactRecord">ContactRecord retrieved from database</param>
 /// <returns></returns>
 public bool IsRecordOwner(ContactRecord contactRecord)
 {
     return contactRecord != null && contactRecord.Owner == Owner;
 }