C#•3y ago

NullReferenceException on FirstorDefault()

 var db = new DatabaseContext();

                var staffMembers = db.StaffMember; // here i get right item 100%
                var temp = staffMembers.Where(x => x.Id == args.User.Id).ToList(); // <-- this returns me my item
                var staffMember = temp.FirstOrDefault(); // <-- System.NullReferenceException
                var stafftemp = temp[0]; // <-- null without any reason

 var db = new DatabaseContext();

                var staffMembers = db.StaffMember; // here i get right item 100%
                var temp = staffMembers.Where(x => x.Id == args.User.Id).ToList(); // <-- this returns me my item
                var staffMember = temp.FirstOrDefault(); // <-- System.NullReferenceException
                var stafftemp = temp[0]; // <-- null without any reason

Any ideas how to solve it?

62 Replies

WaffenOP•3y ago

UPD: var stafftemp = temp[0]; returned me my item

WaffenOP•3y ago

Some additional screenshots to prove, that i have right id in args.User.ID

Unknown User•3y ago

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WaffenOP•3y ago

I know, i did this variant for debug

Unknown User•3y ago

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WaffenOP•3y ago

System.NullReferenceException

Unknown User•3y ago

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WaffenOP•3y ago

Wait a second

WaffenOP•3y ago

Wtf? It just worked now, but i didn't change anything

WaffenOP•3y ago

But third line still not working

Unknown User•3y ago

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WaffenOP•3y ago

after i commented out three lines it broke down again :D

WaffenOP•3y ago

How does it work?)

Unknown User•3y ago

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dancepanda42•3y ago

Maybe the error is in the DatabaseContext class. How is the data provided there?

phaseshift•3y ago

are you sure args & User are not null?

dancepanda42•3y ago

Yes, this could also cause it since temp was not yet executed at this point and the iteration is not executed until FirtstOrDefault. For testing just set args?.User?.Id

WaffenOP•3y ago

Yes, I have previously uploaded screenshots showing that args.user and staff stats is not null I'm pretty sure the problem isn't with the database

WaffenOP•3y ago

🤨

dancepanda42•3y ago

This is a very strange behavior. Ohhh wait a minute. I just noticed that your code continues to run without problems past the NullReferenceException point. Which Visual Studio extension shows you this info on the side? Probably just the extension can not create a reference at development time and comes for this reason to the exception. If you make a try catch block around your code. Does it run into the catch block at all at some point?

WaffenOP•3y ago

ReSharper

dancepanda42•3y ago

It looks to me like resharper shows the error but does not occur in runtime.

WaffenOP•3y ago

VS without resharper runs this code with same result. It's just skip this error (also with try cath) and i can see this error only in debug

dancepanda42•3y ago

The last thing I can think of is that an element in the StaffMember is null. Try to enter a ? after the x. x?.Id == args.User.Id Otherwise, I have no further idea.

WaffenOP•3y ago

It's LinQ. It's can't contains ?

phaseshift•3y ago

linq can Are you actually getting a problem? ie you can see an exception in the locals window, not just in those 'lens' stuff

WaffenOP•3y ago

Yes, i have a check staffMember == null and because of this error, this check is skipped

WaffenOP•3y ago

WaffenOP•3y ago

Because staffMember is not null it is just nothing Idk how does it work

phaseshift•3y ago

show the call stack of the exception

WaffenOP•3y ago

I put this line in try catch but C# just skips this error and doesn't catch it

phaseshift•3y ago

then it's not an error Show the stack trace If you can't, you're chasing hallucinations

WaffenOP•3y ago

How to get stack trace from this without try catch? Sorry i just really don't know

phaseshift•3y ago

$debug

MODiX•3y ago

https://docs.microsoft.com/en-us/visualstudio/get-started/csharp/tutorial-debugger?view=vs-2022

Tutorial: Debug C# code - Visual Studio (Windows)

Learn features of the Visual Studio debugger and how to start the debugger, step through code, and inspect data in a C# application.

phaseshift•3y ago

the stack trace is a property on the exception

phaseshift•3y ago

also click on this to be sure https://www.christianfindlay.com/blog/visual-studio-break-on-all-exceptions

Visual Studio - Break On All Exceptions

Read about breaking on all exceptions in Visual Studio. This enables you to see the exact details of an exception instead of ignoring handled exceptions

phaseshift•3y ago

If there's an exception the debugger stops. You dont need try/catch to see it

WaffenOP•3y ago

Still not working :(

Unknown User•3y ago

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WaffenOP•3y ago

Because i did it for debug

using System.Diagnostics.CodeAnalysis;

namespace StaffStatsBeta.Database;

public class StaffMembers
{
    public ulong Id { get; set; }
    public DateTime JoinDate { get; set; }
    
    public List<OnlineLogs> OnlineLogs { get; set; }
    public List<MainStats> MainStats { get; set; }
}

using System.Diagnostics.CodeAnalysis;

namespace StaffStatsBeta.Database;

public class StaffMembers
{
    public ulong Id { get; set; }
    public DateTime JoinDate { get; set; }
    
    public List<OnlineLogs> OnlineLogs { get; set; }
    public List<MainStats> MainStats { get; set; }
}

Unknown User•3y ago

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WaffenOP•3y ago

public class MainStats 
{
    public int Id { get; set; }

    public DateTime Date { get; set; }

    public StaffMembers StaffMembers { get; set;}

    public int Tickets { get; set; }
    public int Violations { get; set; }
    public int Mutes { get; set; }
    public int Warns { get; set; }
    public int Bans { get; set; }
}

public class StaffMembers
{
    public ulong Id { get; set; }
    public DateTime JoinDate { get; set; }
    
    public List<OnlineLogs> OnlineLogs { get; set; }
    public List<MainStats> MainStats { get; set;}
}

public class OnlineLogs
{
    public int Id { get; set; }
    public StaffMembers StaffMembers { get; set; }

    public DateTime EnterTime { get; set; }
    public DateTime? OutTime { get; set; }

}

public class DatabaseContext : DbContext
{
    public DbSet<StaffMembers> StaffMember { get; set; }
    public DbSet<OnlineLogs> OnlineLogs { get; set; }
    public DbSet<MainStats> MainStats { get; set; }

    public DatabaseContext()
    {
        Database.EnsureCreated();
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        AppContext.SetSwitch("Npgsql.EnableLegacyTimestampBehavior", true);

        // TODO: redo this with json configuration and connectionStringBuilder
        optionsBuilder.UseNpgsql("Host=localhost;Database=testdb;Username=postgres;Password=root");
    }
}

public class MainStats 
{
    public int Id { get; set; }

    public DateTime Date { get; set; }

    public StaffMembers StaffMembers { get; set;}

    public int Tickets { get; set; }
    public int Violations { get; set; }
    public int Mutes { get; set; }
    public int Warns { get; set; }
    public int Bans { get; set; }
}

public class StaffMembers
{
    public ulong Id { get; set; }
    public DateTime JoinDate { get; set; }
    
    public List<OnlineLogs> OnlineLogs { get; set; }
    public List<MainStats> MainStats { get; set;}
}

public class OnlineLogs
{
    public int Id { get; set; }
    public StaffMembers StaffMembers { get; set; }

    public DateTime EnterTime { get; set; }
    public DateTime? OutTime { get; set; }

}

public class DatabaseContext : DbContext
{
    public DbSet<StaffMembers> StaffMember { get; set; }
    public DbSet<OnlineLogs> OnlineLogs { get; set; }
    public DbSet<MainStats> MainStats { get; set; }

    public DatabaseContext()
    {
        Database.EnsureCreated();
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        AppContext.SetSwitch("Npgsql.EnableLegacyTimestampBehavior", true);

        // TODO: redo this with json configuration and connectionStringBuilder
        optionsBuilder.UseNpgsql("Host=localhost;Database=testdb;Username=postgres;Password=root");
    }
}

This is whole my databasecontext I am using EF Core for PostgreSQL btw

phaseshift•3y ago

that is showing a 'debugger evaluation exception'. It is not an exception from the code that ran... but since you're there, please expand args

WaffenOP•3y ago

But i see this 'debugger evaluation exception' only in this place and my variable staffMember is empty only here...

WaffenOP•3y ago

phaseshift•3y ago

you dont know what the value is if the locals evaluation is not working What happens after the if (staffMember == null) line?

WaffenOP•3y ago

Just an discord answer and it's just skip this line with this message:

phaseshift•3y ago

lets ignore all the orange stuff - I dont trust it. You're still on that line. What happens next?

WaffenOP•3y ago

This if just skipped

phaseshift•3y ago

so it's not null So theres no problem

WaffenOP•3y ago

I don't see what's inside this variable

Unknown User•3y ago

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WaffenOP•3y ago

Ok, but why i can get and see this staffMember in another part of my code

WaffenOP•3y ago

Oh, i've read again and you mean staffMembers. I am not trying to check what inside staffMembers, i am trying to check what inside staffMember which i get with FirstOrDefault()

phaseshift•3y ago

well if it works in one place, but not in another, then look at the differences

WaffenOP•3y ago

But there is no diffrerence...

WaffenOP•3y ago

Doesn't work:

Unknown User•3y ago

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phaseshift•3y ago

it doesnt throw in actuality It's just the debugger evaluation

Unknown User•3y ago

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phaseshift•3y ago

Anyway, I'm bored of saying the same thing and waffle showing the same 'problem' that has been explained

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NullReferenceException on FirstorDefault()