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I am updating a quantity in my cart, but it is throwing a Sequence has no elements' exception.

And I don't know what that even means. At first I thought that maybe there was a null value being passed somewhere, but that isn't the case, as I've checked that:

Sequence contains no elements Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidOperationException: Sequence contains no elements

Source Error:

Line 35: var uid = WebSecurity.CurrentUserId; Line 36: var newqty = Request.Form["Quantity"]; Line 37:
OModel.Cart c = (from item in database.Carts Line 38:
where item.UserId == uid && item.PartNumber == pnumber && item.OrderId == oid Line 39: select item).First();

Any ideas what could be causing this?

Arrow
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    You might want to read http://stackoverflow.com/questions/1024559/when-to-use-first-and-when-to-use-firstordefault-with-linq/1024577#1024577 – driis Aug 03 '12 at 19:07
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    @driss I've been using FirstOrDefault() when it should be used, but when I wanted to learn how to Update, I found a blog (the same one that I learned to add and remove from) - and he used First instead of FirstOrDefault(), so I used that instead. But FirstOrDefault() throws another exception. So I wasn't sure which one should be used, or if it even mattered, in this case. – Arrow Aug 03 '12 at 19:13

6 Answers6

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First() is causing this if your select returns 0 rows. You either have to catch that exception, or use FirstOrDefault() which will return null in case of no elements.

Carrie Kendall
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Varius
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    Thank you. That makes sense. I wonder though, why would it be returning _NULL_ - even after I've checked that it does actually exist in the database? Do you know of any other ways to update the item in a table? – Arrow Aug 03 '12 at 19:07
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    You could create Stored Procedure, map it in Linq and call it instead. But I don't see why this wouldn't work, provided all parameters are ok. You could try to use Sql Profiler to see what SQL command is actually executed. That should help finding what is wrong. – Varius Aug 03 '12 at 19:13
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    if it actually does exist in the database and it isnt being returned then it is not satisfying the conditions. are you use UserId == uid && PartNumber == pnumber && OrderId == oid are all true? are you checking for the right types? – c0deNinja Aug 03 '12 at 19:14
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    It returns null because null is the default value. "default(object)" is a C# expression that returns null. "default(int)" returns 0. – Tormod Aug 03 '12 at 19:14
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    In my case i use Single, so i use SingleOrDefault, thank you !. – Bhimbim Dec 14 '17 at 05:18
15

You are using linq's First() method, which as per the documentation throws an InvalidOperationException if you are calling it on an empty collection.

If you expect the result of your query to be empty sometimes, you likely want to use FirstOrDefault(), which will return null if the collection is empty, instead of throwing an exception.

Marty
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5

Instead of .First() change it to .FirstOrDefault()

c0deNinja
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1

The value is null, you have to check why... (in addition to the implementation of the solutions proposed here)

Check the hardware Connections.

user1012506
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1

Part of the answer to 'handle' the 'Sequence has no elements' Exception in VB is to test for empty

If Not (myMap Is Nothing) Then
' execute code
End if

Where MyMap is the sequence queried returning empty/null. FYI

ransems
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0

I had the same issue, i realized i had deleted the default image that was in the folder just update the media missing, on the specific file

anonymous0101
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