C#•2y ago

✅ Cannot resolve scoped service...

What I did wrong? Here's how I injected IQueryHandlers to DI:

services.Scan(selector =>
        {
            selector.FromCallingAssembly()
                .AddClasses(filter => { filter.AssignableTo(typeof(IQueryHandler<,>)); })
                .AsImplementedInterfaces()
                .WithScopedLifetime();
        });

services.Scan(selector =>
        {
            selector.FromCallingAssembly()
                .AddClasses(filter => { filter.AssignableTo(typeof(IQueryHandler<,>)); })
                .AsImplementedInterfaces()
                .WithScopedLifetime();
        });

Injection of dispatchers:

services.AddSingleton<ICommandDispatcher, CommandDispatcher>()
            .Decorate<ICommandDispatcher, CommandDispatcherDecorator>();
        services.AddSingleton<IQueryDispatcher, QueryDispatcher>();

services.AddSingleton<ICommandDispatcher, CommandDispatcher>()
            .Decorate<ICommandDispatcher, CommandDispatcherDecorator>();
        services.AddSingleton<IQueryDispatcher, QueryDispatcher>();

QueryDispatcher:

public class QueryDispatcher : IQueryDispatcher
{
    private readonly IServiceProvider _serviceProvider;

    public QueryDispatcher(IServiceProvider serviceProvider) => _serviceProvider = serviceProvider;

    public Task<TQueryResult> Dispatch<TQuery, TQueryResult>(TQuery query, CancellationToken ct)
    {
        var handler = _serviceProvider.GetRequiredService<IQueryHandler<TQuery, TQueryResult>>();
        return handler.Handle(query, ct);
    }
}

public class QueryDispatcher : IQueryDispatcher
{
    private readonly IServiceProvider _serviceProvider;

    public QueryDispatcher(IServiceProvider serviceProvider) => _serviceProvider = serviceProvider;

    public Task<TQueryResult> Dispatch<TQuery, TQueryResult>(TQuery query, CancellationToken ct)
    {
        var handler = _serviceProvider.GetRequiredService<IQueryHandler<TQuery, TQueryResult>>();
        return handler.Handle(query, ct);
    }
}

3 Replies

demndev•2y ago

Here's a guide from which I wrote this code: https://cezarypiatek.github.io/post/why-i-dont-use-mediatr-for-cqrs/

Cezary Piątek Blog

Why I don't use MediatR for CQRS

Is MediatR really suitable for implementing CQRS pattern?

atakancracker•2y ago

are you trying to resolve scoped service inside singleton service ? both looks like singleton

demndev•2y ago

oh, really. thank you!

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✅ Cannot resolve scoped service...