Generic Request/Handler

[crowz4k]

Hi,

I am trying to make a Generic Request/Handler combination. What I am trying to achieve is to have a generic Request(GetById) where it can be invoked with different entities without having to write more code.

For example, if you look below, I am trying to have a request like this.

public class GetByIdRequest<TEntity, TRes> : IRequest<Result<TRes>>
    where TEntity : class
    where TRes : class
{
    public int Id { get; set; }
    public GetByIdRequest(int id)
    {
        Id = id;
    }
};

public readonly struct Result<TValue>
{
    private readonly ResultState _state;

    public Result(TValue value)
    {
        Value = value;
    }
    [Pure]
    public TValue? Value { get; init; }
} 

Where a request is named GetByIdRequest. Now in the call site, I would specify the exact Entity and an exact result, for example:

_mediator.Send(new GetByIdRequest<ApplicationUser, UserDto>(id));

Handler for the request above looks like this:

public class GetByIdHandler<TEntity,TRes>:
    IRequestHandler<GetByIdRequest<TEntity,TRes>, Result<TRes>>
    where TEntity : class, new() 
    where TRes : class
{
    private readonly AppDbContext _context;
    private readonly IMapper _mapper;

    public GetByIdHandler(AppDbContext context, IMapper mapper)
    {
        _context = context;
        _mapper = mapper;
    }

    public async Task<Result<TRes>> Handle(GetByIdRequest<TEntity, TRes> request, CancellationToken ct)
    {
        var res = await
            _context.Set<TEntity>()
                .ProjectTo<TRes>(_mapper.ConfigurationProvider)
                .FirstOrDefaultAsync(ct);

        return new Result<TRes>(res);
    }
}

When I try to run API, I get the following error:

System.InvalidOperationException: Error constructing handler for request of type 
MediatR.IRequestHandler`2[GetByIdRequest`2[ApplicationUser,UserDto],Result`1[UserDto]]. 
Register your handlers with the container. See the samples in GitHub for examples.
...... 

I did run an automatic scan of the assembly. My question is, do I need to register this handler manually?

I did try with code below but it does not work

srv.AddTransient(typeof(IRequestHandler<,>),typeof(GetByIdHandler<,>)); 

[01Raja]

Hi, Do you have this working?

[zachpainter77]

Another option is to use Reflection. This allows the consumer to use the built in asp.net core DI container.

[crowz4k]

@01Raja Yes with AutoFac. AutoFac can resolve this in runtime.

// DI Register AutoFac modules
builder.Host.ConfigureContainer<ContainerBuilder>(builder =>
{
    builder.RegisterModule(new ApplicationServicesModule());
});

And then adding in ApplicationServicesModule following:

    public class ApplicationServicesModule : Module
    {
        protected override void Load(ContainerBuilder builder)
        {
            builder.RegisterGeneric(typeof(GetByIdHandler<,>)).AsImplementedInterfaces();
        }
    }

[01Raja]

Thanks much.

…

On Sat, Jan 7, 2023, 12:19 PM Vlada ***@***.***> wrote: @01Raja <https://github.com/01Raja> Yes with AutoFac. AutoFac can resolve this in runtime. // DI Register AutoFac modulesbuilder.Host.ConfigureContainer<ContainerBuilder>(builder => { builder.RegisterModule(new ApplicationServicesModule()); }); And then adding in ApplicationServicesModule following: public class ApplicationServicesModule : Module { protected override void Load(ContainerBuilder builder) { builder.RegisterGeneric(typeof(GetByIdHandler<,>)).AsImplementedInterfaces(); } } — Reply to this email directly, view it on GitHub <#778 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AX6U3Q5PDN3TTFKRMJYVHTTWRHFUZANCNFSM57ZP32AQ> . You are receiving this because you were mentioned.Message ID: ***@***.***>