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
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;
}
}
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.
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
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Linq 'Where' Query Returning One Valid Result Plus Multiple Null Values
Jul 06, 2020 11:27 PM|CincySteve|LINK
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
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23587 Posts
Re: Linq 'Where' Query Returning One Valid Result Plus Multiple Null Values
Jul 07, 2020 12:00 AM|mgebhard|LINK
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
Member
26 Points
63 Posts
Re: Linq 'Where' Query Returning One Valid Result Plus Multiple Null Values
Jul 08, 2020 12:57 AM|CincySteve|LINK
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.
Member
10 Points
2 Posts
Re: Linq 'Where' Query Returning One Valid Result Plus Multiple Null Values
Nov 20, 2020 01:35 PM|Daniel Glos|LINK
I'm experiencing the same issue. Were you able to find out something more?
Member
26 Points
63 Posts
Re: Linq 'Where' Query Returning One Valid Result Plus Multiple Null Values
Nov 20, 2020 02:48 PM|CincySteve|LINK
Regrettably NO.
Member
10 Points
2 Posts
Re: Linq 'Where' Query Returning One Valid Result Plus Multiple Null Values
Nov 20, 2020 02:50 PM|Daniel Glos|LINK
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