VB.NET LINQ query on List(Of Object)

Question

I am having trouble with a LINQ query -

 Dim otherRecords As List(Of Objects) = listOf.Where(Function(x) x.ID_NUM = newID _
                                        And (x.Codes.Contains(ddlPrimaryCode.SelectedItem.Text.Trim) And Not x.Codes = Nothing)).ToList()

Error An exception of type 'System.NullReferenceException' occurred in CI.dll but was not handled in user code

Additional information: Object reference not set to an instance of an object.

The problem is the listOf contains the value "Nothing" for the x.Codes.Contains.

Before I had

 Dim otherRecords As List(Of Objects) = listOf.Where(Function(x) x.ID_NUM = newID _
                                                       And (x.Codes.Contains(ddlPrimaryCode.SelectedItem.Text.Trim)).ToList()

And it was crapping out.

I need to be able to return only records with matching ID_NUM and Codes.

read what it means. do you know what a NullReferenceException means? it means that you are trying to use an object that is not initialised/instantiated.... — Ahmed ilyas
– Ahmed ilyas, Commented Mar 10, 2014 at 18:47

Steven Doggart · Accepted Answer · 2014-03-10 18:55:44Z

7

You need to check if it's Nothing first and use the AndAlso keyword to stop it from evaluating the latter statement. AndAlso is short-circuiting. See this link for more information on what that means.

Also, when checking if an object is null, you should use the Is or IsNot operator rather than =. From this MSDN article:

When checking whether a reference (or nullable value type) variable is null, do not use = Nothing or <> Nothing. Always use Is Nothing or IsNot Nothing.

This should work

Dim otherRecords As List(Of Objects) = listOf.Where(Function(x) _
                                                        (x.ID_NUM = newID) AndAlso _
                                                        (x.Codes IsNot Nothing) AndAlso _
                                                        (x.Codes.Contains(ddlPrimaryCode.SelectedItem.Text.Trim()))).ToList()

edited Mar 10, 2014 at 18:55

answered Mar 10, 2014 at 18:49

Steven Doggart

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1 Comment

Moojjoo Over a year ago

Steven you are 100% right, I was just schooled on it from my co-worker... Thank you.

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