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Linq Where Problem

Posted on 2014-04-07
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Last Modified: 2016-02-15
I'm trying to use..

Dim subListItems = From items In listIn Where items.Surname.StartsWith("D")

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but I get

A first chance exception of type 'System.NullReferenceException' occurred

If I remove the where clause there are no problems and I can see items with a surname starting with D.

What is going wrong ?
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Question by:Dodsworth
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6 Comments
 
LVL 23

Expert Comment

by:Jens Fiederer
ID: 39983137
Probably one of the "items" has a null value for surname.
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LVL 23

Accepted Solution

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Jens Fiederer earned 2000 total points
ID: 39983146
you could try
Where items.Surname isnot Nothing andalso items.surname.StartsWith("D")
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LVL 1

Author Comment

by:Dodsworth
ID: 39983198
I don't want to 'ignore' null items though.  Ideally I'd like them to be grouped with items that have a zero length string as a surname.  Is that linq-able?
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LVL 5

Expert Comment

by:jayakrishnabh
ID: 39983278
Dim abc As dynamic = From p In listIn Where p.Name IsNot Nothing Where p.Name.StartsWith("D")
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LVL 23

Expert Comment

by:Jens Fiederer
ID: 39983293
The whole POINT of using a where clause is to ignore items....originally you wanted to ignore all items where the surname did not start with "D".

If you are trying to do groupings you probably should be working with group ... by clauses.

You can adapt pretty much anything to LINQ....you can always write a function that takes an object and does arbitrary processing to do a yes/no (use/ignore) decision (a PREDICATE for a where clause) or that returns some useful value (for a group .. by clause).
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LVL 23

Expert Comment

by:Jens Fiederer
ID: 39983296
Some examples of using grouping operators are at


http://msdn.microsoft.com/en-us/vstudio/bb737908
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