Question

My Question is how do I handle a null set returned from a linq query if I am loading it into a custom class.

example

queryResults = queryResults.Select(p => new specialItems(p.ID, p.SECTION, p.PROGRAM, p.EVENT).ToList<specialItems>();

…

public class specialItems
{
    public string Id { get; set; }
    public string Section { get; set; }
    public string Program { get; set; }
    public string Event { get; set; }

    public courseItems(string id, string section, string program, string event)
    {
        this.Id = id;
        this.Section = section; 
        this.Program = program;
        this.Event = event;
    }
}

Currently this query works great until the result set is empty, then I get:
“Object reference not set to an instance of an object.”

I need the query to return an empty List if the result set is empty.

UPDATE – Asided from the invalid redeclaration of a variable (fixed) I did find that the issue was higher up in the initial construction of the linq query. This became apparent when I received several good suggestions and removed the error. Once I fixed the original query things worked swimmingly.

Answer 1

Use the null coalescing operator (??).

List<specialItems> queryResults = queryResults.Select(p => new specialItems(p.ID, p.SECTION, p.PROGRAM, p.EVENT).ToList<specialItems>() ?? new List<specialItems>();

EDIT: Yeah, looking at what you have there a little closer, it’s the ToList that’s blowing up when this happens. You might have to split it up a bit.

var temp = queryResults.Select(p => new specialItems(p.ID, p.SECTION, p.PROGRAM, p.EVENT);

List<specialItems> results = temp == null ? new List<specialItems>() : temp.ToList<SpecialItems>();

Have to do it this way, because there’s no good spot to put the null coalescing operator in this case.