CODEWITHSUNDEEP
c#linq
Mert
Mert

Reputation: 6572

Linq - Distinct list of object fill in int array

I am trying to do, get randomly one of "list of objects" from all lists. I am getting NullReferenceException I also tried List couldn't make it work.

List<BL.Test.Test> Tests = BL.Test.GET.TestGroup(CategoryId);

// NullReferenceException on the line below:
int[] Groups = Tests.Select(d => d.TestGroupId).Distinct().ToArray(); 

Session["TestGroup"] = Tests.Select(t => t.TestGroupId = Groups[rnd.Next(Groups.Length)]);

Tests not null

Upvotes: 0

Views: 143

Answers (2)

Ankush Madankar
Ankush Madankar

Reputation: 3834

Since TestGroupId would be null hence null.Distinct() throws NullArgumentReference exception. Change ur code with following code:

List<BL.Test.Test> Tests = BL.Test.GET.TestGroup(CategoryId);

int[] Groups = Tests.Where(d=>d.TestGroupId.HasValue).Select(d => d.TestGroupId).Distinct().ToArray(); 

Session["TestGroup"] = Tests.Select(t => t.TestGroupId = Groups[rnd.Next(Groups.Length)]);

Make use of HasValue to find if TestGroupId has some value.

Upvotes: 0

astef
astef

Reputation: 9498

Obviously, BL.Test.GET.TestGroup is the method which returns null.

That's the most probable explanation for a NullReferenceException in a second line of your example.

And if Select, Distinct and ToArray are extension methods declared in System.Linq, this reason is the only possible, so check your method.

UPD.

Sorry guys, I am wrong.

TestGroupId member of BL.Test.Test class is missed.

UPD-2

This is a good example of community debugging question. As I know it is not appreciated here

Upvotes: 2

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