EntityFramework using navigation property to populate computed property - entity-framework

Question

Basically what I want to do is return a read only string (user name) which is dependent on the navigation property User and just concatenates the first and last name together.
Ideally I'd just assign a value to OwnerUserId and then use the navigation property to retrieve the data if this is possible? I want to keep the model class as clean as possible.
Any ideas?
POCO Model
namespace Model
{
public class TicketReply
{
public int TicketReplyId { get; set; }
public string Title { get; set; }
/* ....more.... */
/* User ID FK */
public int OwnerUserId { get; set; }
/* User Navigation property */
[ForeignKey("OwnerUserId")]
[IgnoreDataMember]
public User User { get; set; }
/* Here is where I am stuck.... */
public string UserName
{
get { return User.FirstName + " " + User.LastName; }
set { }
}
}
}
*DB initialiser* - just to give some context
private List<TicketReply> AddReplies(DbContext context)
{
var replies = new List<TicketReply>
{
new TicketReply { TicketReplyId = 1, TicketId = 1, CreatedAt = DateTime.Now, OwnerUserId = 1, Text = "My initial query"},
new TicketReply { TicketReplyId = 2, TicketId = 1, CreatedAt = DateTime.Now, OwnerUserId = 2, Text = "Test reply."},
new TicketReply { TicketReplyId = 3, TicketId = 2, CreatedAt = DateTime.Now, OwnerUserId = 1, Text = "Test query"}
};
replies.ForEach(status => context.TicketReplies.Add(status));
context.SaveChanges();
return replies;
}
Thanks
Arthur

Answer 1

Roughly (and typing from memory)
Make it part of the User, e.g...
public class User
{
[NotMapped] // or from code "modelBuilder.Entity<User>().Ignore(x => x.UserName);"
public string UserName
// your user name implementation
}
You cannot just assign OwnerUserId and expect it to work - User will
be loaded when you load Ticket. Also you don't use 'OwnerUserId' in
your fk-entity - to search for for User.
You can use that to 'set' the User 'it points to' - it's saved when you first do the 'SaveChanges'.
e.g...
var user = new User {First = ... Second=...};
db.Tickets.Add(new Ticket{ User = user, ...});
// or...
db.Tickets.Add(new Ticket{ OwnerUserId = ownerid, ...}); // to point to exisitng one you know exists
db.SaveChanges();
...sometime later on...
var ticket = new Ticket { OwnerUserId = ownerid };
// ticket.User is null - won't work
var ticket = // tickets query // db.Tickets.Where(x => x.TicketId == ticketid).FirstOrDefault();
var username = ticket.User.UserName; // now it works, you have your User loaded
Or explicitely...
var user = db.Users.Where(x => x.UserId == ownerid).FirstOrDefault();
var username = user.UserName;