Select from List

Question

I get null reference with the following code, how do I properly assign the result variable to the new list:

var result = from loan in loansList
             where loan.supervisorID == "1188775"
             select loan;

List<Loan> ayumiLoans = new List<Loan>();

ayumiLoans = result as List<Loan>;

foreach (Loan aLoan in ayumiLoans )
{
    aLoan.printLoan();
}

`List ayumiLoans = result.ToList();` – Kevin Gosse Jan 24 '19 at 07:28 — Kevin Gosse, Jan 24 '19 at 07:28
can you post it as answer not comment please – Coder Jan 24 '19 at 07:37 — Coder, Jan 24 '19 at 07:37

Dmitry Bychenko · Accepted Answer · 2019-01-24T07:37:53.767

result is not of type List<Loan>; the only we can say is that it implements IEnuemrable<Loan>. That's why

 result as List<Loan>;

is null. Then you assign null to ayumiLoans

ayumiLoans = result as List<Loan>; // ayumiLoans is null

And you get the error when trying to loop over null. Try either

var result =   from loan in loansList
              where loan.supervisorID == "1188775"
             select loan;

List<Loan> ayumiLoans = new List<Loan>();

// Add all result items into ayumiLoans
ayumiLoans.AddRange(result);

Or

var result =   from loan in loansList
              where loan.supervisorID == "1188775"
             select loan;

// Materialize result as List<Loan> 
List<Loan> ayumiLoans = result.ToList();

@Coder: you are welcome! – Dmitry Bychenko Jan 24 '19 at 08:04 — Dmitry Bychenko, Jan 24 '19 at 08:04

score 1 · Answer 2 · answered Jan 24 '19 at 07:36

1

I think you should be able to just do it this way:

List<Loan> ayumiLoans = new List<Loan>(result);

Otherwise Im sure Dmitry got it right, he helped me often already :'D

answered Jan 24 '19 at 07:36

Benyom

75
7

score 1 · Answer 3 · answered Jan 24 '19 at 07:50

1

There is a bit more efficient List<T>.FindAll(Predicate<T>) Method for that :

 List<Loan> ayumiLoans = loansList.FindAll(loan => loan.supervisorID == "1188775");

answered Jan 24 '19 at 07:50

Slai

22,144
5
45
53

3 Answers3