Linq 'Where' Query Returning One Valid Result Plus Multiple Null Values

Question

User-343630552 posted

I have a simple Linq query containing:  .Where(x => x.Year == year), where year = 2018.  It is against a List<T> that only has 8 elements, all of which have a valid entry in the Year field.  Only one of the List items has Year == 2018.  But the returned result, which I convert to a list via ToList(), contains 4 elements, including the one with the matching Year and 3 others that show as null.  I am at a loss to explain this behavior.  Any ideas?  The Where query is in a Blazor Wasm component being developed with VS Community 2019, if that makes any difference.  Thanks.  Steve

Answer 1

User475983607 posted

The community will need sample code that reproduces this issue.  

    public class Data
    {
        public int Year { get; set; }
        public string Name { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            List<Data> results = PopluateTestData().Where(m => m.Year == 2018).ToList();
            Console.WriteLine(results.Count());
        }

        public static List<Data> PopluateTestData()
        {
            List<Data> list = new List<Data>();
            for (int i = 0; i < 8; i++)
            {
                list.Add(new Data() { Year = 2012 + i, Name = $"Item {i}"});
            }
            return list;
        }
    }

Results

1

Answer 2

User-343630552 posted

I have not been able to recreate the problem in a demo app.  While I suspect finding an answer will be elusive, here are the circumstances that led up to the Linq Where statement.  I also cannot take screenshots of the variables since I can only see them in the VS debugger whose popups aren't captured in a screenshot.   I apologize for the complexity of all this.  It is part of a demo app where I'm trying to learn how these capabilities work and work together.

As I said originally, the app is a Blazor Wasm one developed in Visual Studio Community 2016.  The data that's in the source List<T> comes from an IndexedDB database object that is read via a Javascript function that's invoked when a button is clicked.  This object is passed to a Blazor component via DotNet.InvokeAsync with the object as a parameter. The Blazor component disassembles the object into various parts including a full List<T>, which is then filtered via a Where clause.   The List<T> is in a Blazor Services data class that enables data sharing across Blazor components.  At this point in the execution, everything looks as I would expect in the VS debugger.

Based on a 2nd button click that invokes another Blazor method, the List<T> in the Services class is assigned to a local List<T>.  This is then assigned to a different local List<T> after filtering with another Where clause.  It's this final Where that returns 4 items, 3 of which show in the VS debugger as null.  

I'm guessing I just needlessly spent the time to describe this because we can't replicate it in a simpler demo app.  Anyway, at least it's in the forum in case anyone else experiences something similar.

Answer 3

User771289253 posted

I'm experiencing the same issue. Were you able to find out something more?

Answer 4

User-343630552 posted

Regrettably NO.

Answer 5

User771289253 posted

I think this is just a debugging issue. Because when I log the length of the list it logs the correct length without including the null objects. Just when I try to inspect the collection inside visual studio it shows the nulls