Handling 'Sequence has no elements' Exception

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?

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最佳答案

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.

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

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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.

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

Check the hardware Connections.

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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

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I also faced the same issue but I was not using First(), instead, I was using ToListAsync(). My issue was that I had not made the attributes in my entity class public. Making them public solved my issue.

Before :

string name {get; set;}

After :

public string name {get; set;}