Linq null reference value match from database id

Question

in my code there is a ddlitemid that can be null and in Linq query my code is like

valuecheck = _allQuestions.Where(x => x.nID == ddlItemId).FirstOrDefault().strName;

if ddlitemid not exist in my database it gives error i wants to handle null reference object error

You should probably look at this question/answer here first: http://stackoverflow.com/questions/15948369/how-to-handle-null-values-in-linq - I think that's what you are looking for? — joshmcode, Mar 19 '15 at 18:21
hi i saw that earlier my pattern is different than that question so that's why i ask question ok — raja atif, Mar 20 '15 at 06:24

score 2 · Answer 1 · answered Mar 19 '15 at 18:20

Then separate the call to FirstOrDefault from the access of strName. Also you can remove the Where and put the lambda filter into the FirstOrDefault.

var quesiton = _allQuestions.FirstOrDefault(x => x.nID == ddlItemId);
if(question != null)
{
    valuecheck = question.strName;
}

score 2 · Accepted Answer · answered Mar 19 '15 at 21:38

I see this pattern FirstOrDefault().SomeProperty very often. It has two drawbbacks.

You always need to do a null check on FirstOrDefault().
It is not efficient.

About the second point: FirstOrDefault() grabs a whole entity from the database and you use only one field from it. You can kill two birds with one stone by doing:

valuecheck = _allQuestions.Where(x => x.nID == ddlItemId)
                          .Select(q => q.strName)
                          .FirstOrDefault();

Or .FirstOrDefault() ?? string.Empty.

score 1 · Answer 3 · answered Mar 19 '15 at 18:19

The way I normally handle this is to assign my linq results to a variable and then check for null.

var tempStorage = _allQuestions.Where(x => x.nID == ddlItemId).FirstOrDefault();

if(tempStorage != null)
{
    valuecheck = tempStorage.strName;
}

This way you don't have to worry about the null ref exception since you check the existence first.

Linq null reference value match from database id

3 Answers3