Need help with a LINQ ArgumentOutOfRangeException in C#

Question

Hi there,

Hoping this is a nice softball of a question for a friday but I have the following line of code:

//System.ArgumentOutOfRangeException generated if there is no matching data
currentAnswers = new CurrentAnswersCollection()
    .Where("PARTICIPANT_ID", 10000).Load()[0];

CurrentAnswersCollection is a strongly-typed collection populated by a view going back to my database. The problem of course is that if there is not a corresponding PARTICIPANT_ID = 10000 I get the error message.

Is there a better way to write this so that I wouldn't get the error message at all? I just dont know enough about LINQ syntax to know if I can test for the existance first?

thanks.

Answer 1

Use this:

currentAnswers = new CurrentAnswersCollection()
    .Where("PARTICIPANT_ID", 10000).Load()
    .FirstOrDefault();

It'll return null if there is no first element.

But you may need to fix your code (replicated here) first - the .Where syntax looks dodgy.

Answer 2

You need a lambda expression in .Where.

currentAnswers = new CurrentAnswersCollection().Where(c => c.PARTICIPANT_ID == 10000).Load().FirstOrDefault(); 

Answer 3

Try:

var answers = new CurrenAnswersCollection().Where("PARTICIPANT_ID", 10000);
if(answers.Count() >= 1) currentAnswers = answers.Load()[0];

or something similar.

Answer 4

The ArgumentOutOfRangeException is occurring when you try to use the indexer to get the first item from the (empty) list. Using the FirstOrDefault() extension method is a convenient way to return the first element of a collection, if there is one, otherwise to return null.

currentAnswers = new CurrentAnswersCollection().Where("PARTICIPANT_ID", 10000)
                                               .Load()
                                               .FirstOrDefault();

http://msdn.microsoft.com/en-us/library/system.linq.enumerable.firstordefault.aspx