Question

I get a list of all users in my database with the following code:

IEnumerable<Firma> firmaer = db.Firma.ToList();

I try to map each user to a ViewModel that looks like this:

public class UserViewModel
{
    public String CVR_Nummer { get; set; }
    public DateTime LastActivityDate { get; set; }
    public DateTime CreationDate { get; set; }
    public String FirmaNavn { get; set; }

}

When the field firma_navn in the datbase is empty, i get a NullReferenceException

model.FirmaNavn = firmaer.Where(x => x.CVR_nummer == user.UserName).FirstOrDefault().firma_navn ?? "Missing";

It throws a NullReferenceException.

I can catch this exception, but i have heard somewhere that catching exceptions is kind of heavy.

What i would like to do is make

model.FirmaNavn = "Missing";

If the field is empty in the database.

Is this possible without catching the exception, or am i wrong about catching exception is heavy?

EDIT

This is how the method looks like now (after help):

public List<UserViewModel> MapUserViewModel(MembershipUserCollection users)
        {
            List<UserViewModel> userviewmodel = new List<UserViewModel>();

            IEnumerable<Firma> firmaer = db.Firma.ToList();

            foreach (MembershipUser user in users)
            {
                UserViewModel model = new UserViewModel();
                model.CVR_Nummer = user.UserName;
                model.CreationDate = user.CreationDate;
                model.LastActivityDate = user.LastActivityDate;

                var firma = firmaer.Where(x => x.CVR_nummer == user.UserName).FirstOrDefault();

                if (firma != null)
                {
if(string.IsNullOrEmpty(firma.firma_navn))
                        model.FirmaNavn = "Missing";
else
model.FirmaNavn = firma.firma_navn;
                }

                /*if (firmaer != null)
                {
                    var firma = firmaer.Where(x => x.CVR_nummer == user.UserName).FirstOrDefault();
                    model.FirmaNavn = firma.firma_navn ?? "Mangler";   
                }
                */
                userviewmodel.Add(model);
            }
            return userviewmodel;
        }

Now works. Thanks.

Answer 1

You are not wrong about catching exceptions being “heavy” – and they should really only be used for the truly exceptional circumstances.

If firma_navn is likely to be null then it’s not an exceptional circumstance, so you should code accordingly:

if (firmaer != null)
{
    var model = firmaer.Where(x => x.CVR_nummer == user.UserName).FirstOrDefault();
    if (model != null)
    {
        model.FirmaNavn = model.firma_navn ?? "Missing";
    }
}