AspNet.KickStarter.CQRS 1.2.2

AspNet.KickStarter.CQRS

This library provides the following basic interfaces used to implement CQRS with MediatR

• ICommand and ICommandHandler
• IQuery and IQueryHandler

These commands and queries rely on Result, Result<T> and Error types from this library, these types support implicit conversions for ease of use.

The Result class provides Switch and Match methods to conditionally perform actions depending on success or error of the result. They also provide access to the Value or Error values.

The Error class supports FluentValidation errors and provides an AsHttpResult method to produce a suitable IResult from a HTTP handler. For example:

var result = await _mediator.Send(new GetSomeQuery());
return result.Match(
    success => Results.Ok(success),
    error => error.AsHttpResult());

If the unsuccessful result contains a ValidationResult then this will return Results.ValidationProblem with the details, otherwise Results.Problem

TracePipelineBehavior

The library provides a generic TracePipelineBehavior class that adds automatic trace activities for any commands or queries. This can be registered as follows:

builder.Services
    .AddMediatR(_ => _.RegisterServicesFromAssembly(Assembly.GetExecutingAssembly()))
    .AddTracePipelineBehavior();

ValidationPipelineBehavior

The library provides a generic ValidationPipelineBehavior class that enables use of FluentValidation for any commands or queries with a corresponding validator class. This can be registered as follows:

builder.Services
    .AddMediatR(_ => _.RegisterServicesFromAssembly(Assembly.GetExecutingAssembly()))
    .AddValidationPipelineBehavior()
    .AddValidatorsFromAssembly(Assembly.GetExecutingAssembly(), includeInternalTypes: true);

Sample Usage

public record GetDoubleQuery(double Value) : IQuery<double>;

internal async Task<IResult> GetDoubleAsync(double value)
{
    var result = await _mediator.Send(new GetDoubleQuery(value));
    return result.Match(
        success => Results.Ok(success),
        error => error.AsHttpResult());
}

internal class GetDoubleQueryValidator : AbstractValidator<GetDoubleQuery>
{
    public GetDoubleQueryValidator()
    {
        RuleFor(_ => _.Value)
            .GreaterThanOrEqualTo(0)
            .LessThanOrEqualTo(10);
    }
}

internal class GetDoubleQueryHandler : IQueryHandler<GetDoubleQuery, double>
{
    public Task<Result<double>> Handle(GetDoubleQuery request, CancellationToken cancellationToken)
    {
        Result<double> result;
        try
        {
            result = 2 * request.Value;
        }
        catch (Exception ex)
        {
            result = ex;
        }
        return Task.FromResult(result);
    }
}