C#•11mo ago

Interface using functional `Match` does not work

I'm using the OneOf library for discriminated unions

 private static async Task<Results<Created<CustomerResult>, NotFound>> CreateCustomer(
    [FromBody] CreateCustomerParameters parameters, CustomerService customerService
)
{
    // this is OneOf<CustomerResult, ValueNotFound>
    var result = await customerService.CreateCustomerAsync(parameters);

    return result.Match<IResult>
        (x => TypedResults.Created($"/customers/{x.Id}", x), _ => TypedResults.NotFound());
}

 private static async Task<Results<Created<CustomerResult>, NotFound>> CreateCustomer(
    [FromBody] CreateCustomerParameters parameters, CustomerService customerService
)
{
    // this is OneOf<CustomerResult, ValueNotFound>
    var result = await customerService.CreateCustomerAsync(parameters);

    return result.Match<IResult>
        (x => TypedResults.Created($"/customers/{x.Id}", x), _ => TypedResults.NotFound());
}

I have to use TypedResults in order to get OpenAPI to understand things. For those unaware of the library Match works as public TResult Match<TResult>(Func<T0,TResult> f0, Func<T1,TResult> f1) So it will either call the first lambda if CreateCustomerAsync returns a CustomerResult or the second lambda if it returns ValueNotFound TypedResults.Created and TypedResults.NotFound() both extend the IResult interface, so I hoped it would work but it seems like it doesn't

Cannot convert expression type 'Microsoft.AspNetCore.Http.IResult' to return type 'Microsoft.AspNetCore.Http.HttpResults.Results<Microsoft.AspNetCore.Http.HttpResults.Created<Support.Features.Customers.CreateCustomer.CreateCustomerResponse>,Microsoft.AspNetCore.Http.HttpResults.NotFound>'

31 Replies

mg•11mo ago

The types in your return type and the type passed to Match aren't the same

UltraWelfareOP•11mo ago

I know but since both Created and NotFound extend the same interface, shouldn't it work ? 😦

mg•11mo ago

I'm not sure about the details of Match. I've run into a similar problem with OneOf But if Match is returning an IResult, that's what your method needs to return

UltraWelfareOP•11mo ago

I guess it can't cast it back to Results<> then

mg•11mo ago

You need to get Match to return a Results<Created<CustomerResult>, NotFound>> Yeah, certainly not implicitly Let me see how I did this with OneOf

UltraWelfareOP•11mo ago

I casted it, and it simply went boom I used this inside Match<> and it exploded inside the first lambda: Cannot convert expression type 'Microsoft.AspNetCore.Http.HttpResults.Created<Support.Entities.Customer>' to return type 'Microsoft.AspNetCore.Http.HttpResults.Results<Microsoft.AspNetCore.Http.HttpResults.Created<Support.Features.Customers.CreateCustomer.CreateCustomerResponse>,Microsoft.AspNetCore.Http.HttpResults.NotFound>' It can't convert Created into Results

mg•11mo ago

This is an API endpoint right?

UltraWelfareOP•11mo ago

Yeah! using minimal api

mg•11mo ago

Make the method return IResult I think that's what it should be returning anyway

UltraWelfareOP•11mo ago

This breaks OpenAPI

mg•11mo ago

This is my endpoint's entire body

                var result = await itemService.GetByIdAsync(id, token);
                return result.Match(
                    item => Results.Ok(((Material)item).MapToResponse()),
                    notFound => Results.NotFound());

                var result = await itemService.GetByIdAsync(id, token);
                return result.Match(
                    item => Results.Ok(((Material)item).MapToResponse()),
                    notFound => Results.NotFound());

UltraWelfareOP•11mo ago

I have to use TypedResults in order to get OpenAPI to understand things. that's why I said this hahaha

mg•11mo ago

Ahhh right This is the exact problem I had let me see which endpoint it was Oh wait this is that endpoint Here's the whole endpoint

        app.MapGet(ApiEndpoints.Inventory.Items.Materials.Get, async (
                int id,
                [FromServices] IItemService itemService,
                CancellationToken token) =>
            {
                var result = await itemService.GetByIdAsync(id, token);
                return result.Match(
                    item => Results.Ok(((Material)item).MapToResponse()),
                    notFound => Results.NotFound());
            })
            .Produces<MaterialResponse>()
            .Produces(404)
            .WithName(Name);

        app.MapGet(ApiEndpoints.Inventory.Items.Materials.Get, async (
                int id,
                [FromServices] IItemService itemService,
                CancellationToken token) =>
            {
                var result = await itemService.GetByIdAsync(id, token);
                return result.Match(
                    item => Results.Ok(((Material)item).MapToResponse()),
                    notFound => Results.NotFound());
            })
            .Produces<MaterialResponse>()
            .Produces(404)
            .WithName(Name);

I think using Produces is how I worked around it

UltraWelfareOP•11mo ago

That's not a bad idea tbh

mg•11mo ago

Yeah, I think the only issue is that for whatever reason, that doesn't work with multiple codes Although it should with multiple invocations Produces<TNotFound>(404), Produces<TBadRequest>(400), etc

UltraWelfareOP•11mo ago

The only thing I don't like about Produces is that you can mess up the IResult and you'll have no compiler to complain

mg•11mo ago

Yeah this is weird Cause you're right that the typed results implement IResult so they should work I gotta go for now but I'm interested in this myself now so I'll get back to it later if you haven't solved it lol

Thinker•11mo ago

Yeah the compiler in this case sees two conflicting possibilities for the type of TResult. You have to explicitly specify that TResult is IResult for this to work.

UltraWelfareOP•11mo ago

That's the problem.. it doesn't work

        return result.Match<IResult>
            (x => (IResult)TypedResults.Created($"/customers/{x.Id}", x), _ => (IResult)TypedResults.NotFound());

        return result.Match<IResult>
            (x => (IResult)TypedResults.Created($"/customers/{x.Id}", x), _ => (IResult)TypedResults.NotFound());

not even this works it says that the cast is redundant

Thinker•11mo ago

Does it not compile or does it just give you those redundancy warnings?

UltraWelfareOP•11mo ago

Not compile

Cannot convert expression type 'Microsoft.AspNetCore.Http.IResult' to return type 'Microsoft.AspNetCore.Http.HttpResults.Results<Microsoft.AspNetCore.Http.HttpResults.Created<Support.Features.Customers.CreateCustomer.CreateCustomerResponse>,Microsoft.AspNetCore.Http.HttpResults.NotFound>'

Thinker•11mo ago

That's... odd

UltraWelfareOP•11mo ago

public sealed class Results<[DynamicallyAccessedMembers(ResultsOfTHelper.RequireMethods)] TResult1, [DynamicallyAccessedMembers(ResultsOfTHelper.RequireMethods)] TResult2> : IResult, INestedHttpResult, IEndpointMetadataProvider
    where TResult1 : IResult
    where TResult2 : IResult
{

public sealed class Results<[DynamicallyAccessedMembers(ResultsOfTHelper.RequireMethods)] TResult1, [DynamicallyAccessedMembers(ResultsOfTHelper.RequireMethods)] TResult2> : IResult, INestedHttpResult, IEndpointMetadataProvider
    where TResult1 : IResult
    where TResult2 : IResult
{

🤔 the problem is casting it back to the Results of the return

Thinker•11mo ago

Wait you're returning Results<Created<CustomerResult>> from the lambda

UltraWelfareOP•11mo ago

the Match<IResult> works yes

Thinker•11mo ago

So then yeah you quite obviously cannot convert IResult to that (as already mentioned)

UltraWelfareOP•11mo ago

I want to :((((((

Thinker•11mo ago

It doesn't make sense You can't implicitly convert an interface to a concrete type

UltraWelfareOP•11mo ago

how else should I go about doing it turns out i was returning the wrong type from the service:) All you have to do is

 private static async Task<Results<Created<CustomerResult>, NotFound>> CreateCustomer(
    [FromBody] CreateCustomerParameters parameters, CustomerService customerService
)
{
    // this is OneOf<CustomerResult, ValueNotFound>
    var result = await customerService.CreateCustomerAsync(parameters);

    return result.Match<Results<Created<CustomerResult>, NotFound>> // <--- type here
        (x => TypedResults.Created($"/customers/{x.Id}", x), _ => TypedResults.NotFound());
}

 private static async Task<Results<Created<CustomerResult>, NotFound>> CreateCustomer(
    [FromBody] CreateCustomerParameters parameters, CustomerService customerService
)
{
    // this is OneOf<CustomerResult, ValueNotFound>
    var result = await customerService.CreateCustomerAsync(parameters);

    return result.Match<Results<Created<CustomerResult>, NotFound>> // <--- type here
        (x => TypedResults.Created($"/customers/{x.Id}", x), _ => TypedResults.NotFound());
}

type it there it was just that I didn't return CustomerResult from the service, accidently:) That's why it wasn't working:) i'm dumb:)

mg•11mo ago

Oh ok, my issue months ago was that I was trying to just cast what Match returns instead of calling Match<IResult>

UltraWelfareOP•11mo ago

nope just pass the return type inside match as it's generic argument and it's fine although a bit verbose 😢

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Interface using functional `Match` does not work