Using Equals with LINQ on an IEnumerable

Question

this code :

var allSubjectsForAStudent =    GetAllSubjects<Subject>(studentId);

returns an

IEnumerable<Subject>

and I can see bunch of subjects returned in the debugger.

Want to check for a particular Subject doing a case insensitive comparison.

This is the code that I have:

var studentSubjects = allSubjectsForAStudent.Where(s => s.Name.Equals(subjectName, StringComparison.CurrentCultureIgnoreCase));

'subjectName' is a parameter that the method will recieve.

When this line executes I get the 'Object not set to an instance of an object' error.

So what I want to do is a CASE INSENSITIVE search and return the first item when there are more than one and return an empty collection when there are none.

Any clues?

Edit 1

The answers suggest that there can be an entry in the first collection which might have a 'null'. While the observation is true the program makes sure that the 'Subject Name' can not be a null value. Hope this helps.

Thanks in advance.

Is there an item in the collection that's name is `null`? That's the most likely cause. — MarcinJuraszek, Jun 01 '15 at 06:12
I'm tempted to close as duplicate of [What is a NullReferenceException and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it)... but I'm compelled to tell you that you haven't shown us enough code to even diagnose a problem. The problem is in how you got your subjects. Something there is `null` but there's no way of us knowing because you haven't shown us any of that code. — Jeff Mercado, Jun 01 '15 at 06:13

GeorgDangl · Accepted Answer · 2015-06-01T06:42:41.183

0

You could try:

var studentSubjects = allSubjectsForAStudent.Where(s => !string.IsNullOrWhiteSpace(s.Name) && s.Name.ToUpperInvariant() == subjectName.ToUpperInvariant()).FirstOrDefault();

This will either set studentSubjects to null or the first instance in the IEnumerable that matches.

You're getting a NullReferenceException when you call

s.Name.Equals(subjectName)

for an object where s.Name is null.

edited Jun 01 '15 at 06:42

answered Jun 01 '15 at 06:14

GeorgDangl

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Rosenheimer, this gives 'Sequence Contains No Elements' when there is no match. – Codehelp Jun 01 '15 at 06:31
I fixed it, I should have used FirstOrDefault instead of only First. Should be working now. – GeorgDangl Jun 01 '15 at 06:37

Thirisangu Ramanathan · Answer 2 · 2015-06-01T06:37:56.083

0

It will :

if(allSubjectsForAStudent!=null && !string.IsNullorEmpty(subjectName))
var studentSubjects = allSubjectsForAStudent.Where(s => s.Name.Equals(subjectName, StringComparison.CurrentCultureIgnoreCase)).FirstOrDefault();

edited Jun 01 '15 at 06:37

answered Jun 01 '15 at 06:28

Thirisangu Ramanathan

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Using Equals with LINQ on an IEnumerable

2 Answers2