C#•2w ago

Possible NullReferenceException

I've created the following extension method:

public static class QueryableExtensions
{
    public static IQueryable<TSource> WhereIf<TSource>(
        this IQueryable<TSource> source,
        bool condition,
        Expression<Func<TSource, bool>> predicate)
    {
        ArgumentNullException.ThrowIfNull(source);
        ArgumentNullException.ThrowIfNull(predicate);
        
        return condition
            ? source.Where(predicate)
            : source;
    }

    public static IQueryable<TSource> WhereIfElse<TSource>(
        this IQueryable<TSource> source,
        bool condition,
        Expression<Func<TSource, bool>> predicateIf,
        Expression<Func<TSource, bool>> predicateElse)
    {
        ArgumentNullException.ThrowIfNull(source);
        ArgumentNullException.ThrowIfNull(predicateIf);
        ArgumentNullException.ThrowIfNull(predicateElse);
        
        return condition
            ? source.Where(predicateIf)
            : source.Where(predicateElse);
    } 
}

public static class QueryableExtensions
{
    public static IQueryable<TSource> WhereIf<TSource>(
        this IQueryable<TSource> source,
        bool condition,
        Expression<Func<TSource, bool>> predicate)
    {
        ArgumentNullException.ThrowIfNull(source);
        ArgumentNullException.ThrowIfNull(predicate);
        
        return condition
            ? source.Where(predicate)
            : source;
    }

    public static IQueryable<TSource> WhereIfElse<TSource>(
        this IQueryable<TSource> source,
        bool condition,
        Expression<Func<TSource, bool>> predicateIf,
        Expression<Func<TSource, bool>> predicateElse)
    {
        ArgumentNullException.ThrowIfNull(source);
        ArgumentNullException.ThrowIfNull(predicateIf);
        ArgumentNullException.ThrowIfNull(predicateElse);
        
        return condition
            ? source.Where(predicateIf)
            : source.Where(predicateElse);
    } 
}

public sealed class GetAllBotsQueryHandler(IAppDbContext dbContext)
    : IRequestHandler<GetAllBotsQuery, IReadOnlyList<Bot>>
{
    public async Task<IReadOnlyList<Bot>> Handle(GetAllBotsQuery request, CancellationToken cancellationToken)
    {
        return await dbContext.Bots
            .AsNoTracking()
            .Include(x => x.User)
            .Include(x => x.Exchange)
            .WhereIf(request.UserId.HasValue, x => x.UserId == request.UserId.Value)
            .ToListAsync(cancellationToken);
    }
}

public sealed class GetAllBotsQueryHandler(IAppDbContext dbContext)
    : IRequestHandler<GetAllBotsQuery, IReadOnlyList<Bot>>
{
    public async Task<IReadOnlyList<Bot>> Handle(GetAllBotsQuery request, CancellationToken cancellationToken)
    {
        return await dbContext.Bots
            .AsNoTracking()
            .Include(x => x.User)
            .Include(x => x.Exchange)
            .WhereIf(request.UserId.HasValue, x => x.UserId == request.UserId.Value)
            .ToListAsync(cancellationToken);
    }
}

request.UserId.Value:

Nullable value type can be null

Why it doesn't notice the request.UserId.HasValue? Is there an attribute I have to add or smt

20 Replies

Thinker•2w ago

What does WhereIf come from?

HulkstanceOP•2w ago

it's an extension right above

Thinker•2w ago

oh I'm blind lol

HulkstanceOP•2w ago

I've defined it myself

Thinker•2w ago

Nullability analysis can't flow between lambdas like that

HulkstanceOP•2w ago

is there a way I could specify an attribute like NotNullWhen or smt I guess the question is how do I tell the nullability analysis to evaluate the condition boolean?

Thinker•2w ago

You can't, there's no attribute which specifies the kind of flow that the lambda will only execute if the condition is true/false

HulkstanceOP•2w ago

ugh, I guess I'll keep it .WhereIf(request.UserId.HasValue, x => x.UserId == request.UserId) in that case

Unknown User•2w ago

Message Not Public

HulkstanceOP•2w ago

the official .Where implementation from IQueryable doesn't either

Unknown User•2w ago

Message Not Public

SleepWellPupper•2w ago

Why not WhereIf(request.UserId.HasValue, x => x.UserId == request.UserId!.Value)?

HulkstanceOP•2w ago

yeah that works too yeah, looks like

Unknown User•2w ago

Message Not Public

SleepWellPupper•2w ago

OfType<T>() does that

Thinker•2w ago

You can very easily add that yourself

Unknown User•2w ago

Message Not Public

Thinker•2w ago

There's also an issue to allow nullability to flow through Where iirc

Unknown User•2w ago

Message Not Public

Thinker•2w ago

It would also require special versions for value types and reference types

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Possible NullReferenceException

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