C#•4d ago

Generic IH Handlers?

I have a json polymorphic type and I depending on where I'm using it, I want to get a different result type. I have two implementations, the top one works but the bottom one seems cleaner but doesn't work. Are generic handlers possible or do I need to stick to method A here

// THIS ONE WORKS
[Handler]
[AutoConstructor]
public sealed partial class LoadPolymorphObject
{
    private readonly IDbContextFactory<ApplicationDbContext> _dbContextFactory;

    public sealed record Request(int pk, Type targetType);

    private async ValueTask<TObject> HandleAsync(Request request, CancellationToken ct)
    {
        ApplicationDbContext db = await _dbContextFactory.CreateDbContextAsync(ct);
        
        ObjectBase? obj = await db.Table.FindAsync(
            request.pk,
            cancellationToken: ct
        );

        return obj.GetType() == request.targetType
            ? obj
            : throw new InvalidCastException();
    }
}


// THIS ONE DOESNT 
[Handler]
[AutoConstructor]
public sealed partial class LoadPolymorphObject(ApplicationDbContext db)
{
    private readonly IDbContextFactory<ApplicationDbContext> _dbContextFactory;
    public sealed record Request(int pk);

    private async ValueTask<TObject> HandleAsync<TObject>(Request request, CancellationToken ct) where TObject : ObjectBase
    {
        ApplicationDbContext db = await _dbContextFactory.CreateDbContextAsync(ct);
        
        FoundObject? obj = await db.Table.FindAsync(request.pk, cancellationToken: ct
        );

        return obj is TObject ? obj : throw new InvalidCastException();
    }
}

// THIS ONE WORKS
[Handler]
[AutoConstructor]
public sealed partial class LoadPolymorphObject
{
    private readonly IDbContextFactory<ApplicationDbContext> _dbContextFactory;

    public sealed record Request(int pk, Type targetType);

    private async ValueTask<TObject> HandleAsync(Request request, CancellationToken ct)
    {
        ApplicationDbContext db = await _dbContextFactory.CreateDbContextAsync(ct);
        
        ObjectBase? obj = await db.Table.FindAsync(
            request.pk,
            cancellationToken: ct
        );

        return obj.GetType() == request.targetType
            ? obj
            : throw new InvalidCastException();
    }
}


// THIS ONE DOESNT 
[Handler]
[AutoConstructor]
public sealed partial class LoadPolymorphObject(ApplicationDbContext db)
{
    private readonly IDbContextFactory<ApplicationDbContext> _dbContextFactory;
    public sealed record Request(int pk);

    private async ValueTask<TObject> HandleAsync<TObject>(Request request, CancellationToken ct) where TObject : ObjectBase
    {
        ApplicationDbContext db = await _dbContextFactory.CreateDbContextAsync(ct);
        
        FoundObject? obj = await db.Table.FindAsync(request.pk, cancellationToken: ct
        );

        return obj is TObject ? obj : throw new InvalidCastException();
    }
}

8 Replies

Angius•4d ago

https://github.com/ImmediatePlatform/Immediate.Handlers/issues/59

GitHub

Support for generic handlers · Issue #59 · ImmediatePlatform/Imme...

Given a structure that looks something like this public abstract record Message { } public record SomeMessage : Message { } public record OtherMessage : Message { } There is currently no way of han...

Angius•4d ago

And gonna CC @viceroypenguin right quick as well

viceroypenguin•4d ago

didn't we end up deciding that generic handlers weren't going to be as useful as we thought? i haven't even explored it since our conversation

Angius•4d ago

I'm honestly not sure tbh. I think I eventually did move away from needing a generic handler... somehow Been a while

viceroypenguin•4d ago

huh, you didn't open that ticket, and the guy who did isn't on the server anymore iirc, there was some difficulty in dealing with the call-tree through behaviors and such because now it's harder to validate what types are possible in behaviors, etc.

KevSOP•4d ago

I will admit its a pretty niche use case. What I'm doing right now does work so its nbd I just thought I should bring it up

viceroypenguin•4d ago

yeah, it's a known corner case, but doesn't seem to be a big enough problem to justify the work involved in addressing it

KevSOP•4d ago

Totally fair.

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Generic IH Handlers?

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