CODEWITHSUNDEEP
c#asp.net-core.net-corefluentvalidationmediatr
DevOverflow
DevOverflow

Reputation: 491

ASP.NET Core API, Mediatr send method raises exception unable to resolve service for type

I have a ASP.NET Core API, where I am trying to use FluentValidation with Mediatr.

Currently when the controller method is attempting to call Send on the mediatr instance it generates:

Exception thrown: 'System.InvalidOperationException' in Microsoft.Extensions.DependencyInjection.dll: 'Unable to resolve service for type 'GetApplicationQuery' while attempting to activate 'GetApplicationQueryValidator'.'

The query, validator and response class look like this:

public class GetApplicationQuery : IRequest<Response>
{
    private string _name;
    public GetApplicationQuery(string name)
    {
        _name = name;
    }

    public string Name { get { return _name; } }
}

public class GetApplicationQueryHandler : IRequestHandler<GetApplicationQuery, Response>
{

    public GetApplicationQueryHandler() { }

    public async Task<Response> Handle(GetApplicationQuery request, CancellationToken cancellationToken)
    {
        return new Response("yadda yadda");            
    }
}

public class GetApplicationQueryValidator : AbstractValidator<GetApplicationQuery>
{
    public GetApplicationQueryValidator(GetApplicationQuery request)
    {   
        RuleFor(m => m.Name).MinimumLength(30).WithMessage("Name must be greater than 30 characters, long");
    }
}

public class Response
{
    private readonly IList<string> _messages = new List<string>();

    public IEnumerable<string> Errors { get; }
    public object Result { get; }

    public Response() => Errors = new ReadOnlyCollection<string>(_messages);

    public Response(object result) : this() => Result = result;

    public Response AddError(string message)
    {
        _messages.Add(message);
        return this;
    }
}

The configuration I have in the Startup class looks like this:

public void ConfigureServices(IServiceCollection services)
{
    AddMediatr(services);
    services.AddMvc().AddFluentValidation(fv => 
        {
            fv.RegisterValidatorsFromAssemblyContaining<Startup>();
            fv.RunDefaultMvcValidationAfterFluentValidationExecutes = false;
        }).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);           
}

private static void AddMediatr(IServiceCollection services)
{
    const string applicationAssemblyName = "ApplicationApi";
    var assembly = AppDomain.CurrentDomain.Load(applicationAssemblyName);

    AssemblyScanner
        .FindValidatorsInAssembly(assembly)
        .ForEach(result => services.AddScoped(result.InterfaceType, result.ValidatorType));

    services.AddScoped(typeof(IPipelineBehavior<,>), typeof(ValidatorHandler<,>));

    services.AddMediatR(assembly);


}

I am guessing I have the configuration wrong but I have been changing configuration several times with no success.

Any guidance would be much appreciated

Upvotes: 0

Views: 732

Answers (1)

Nkosi
Nkosi

Reputation: 247008

GetApplicationQueryValidator is taking GetApplicationQuery as a constructor dependency but the collection doesn't know about it to be able to inject it.

Also not seeing how it is to be used in that validator. I would suggest removing GetApplicationQuery from the constructor since it doesn't look like it is needed.

public class GetApplicationQueryValidator : AbstractValidator<GetApplicationQuery> {
    public GetApplicationQueryValidator() { 
        RuleFor(m => m.Name).MinimumLength(30).WithMessage("Name must be greater than 30 characters, long");
    }
}

Upvotes: 1

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