Koto.Application

CQRS dispatcher, pipeline behaviors, and cross-service integration abstractions.

Install

dotnet add package Koto.Application

What's included

Type	Purpose
`ICommand` / `ICommand<TResult>`	Marker interfaces for write operations (`ICommandBase`)
`IQuery<TResult>`	Marker interface for read operations (`IQueryBase`)
`ICommandHandler<T>` / `ICommandHandler<T, TResult>`	Command handler contracts
`IQueryHandler<TQuery, TResult>`	Query handler contract
`ICqrsDispatcher`	Dispatches commands and queries to registered handlers
`IPipelineBehavior<TRequest, TResponse>`	Middleware for the CQRS pipeline
`KotoApplicationOptions`	Opt-in behavior registration (`AddLoggingBehavior()`, `AddTransactionBehavior()`, `AddBehavior(type)`)
`LoggingBehavior<,>`	Logs every command/query with timing
`TransactionBehavior<,>`	Wraps each command in a `IUnitOfWork` transaction
`IUnitOfWork`	Abstraction for committing a database transaction
`IRepository<TAgg, TId>`	Persistence contract for aggregates (pairs with `IUnitOfWork`)
`IIntegrationEvent` / `IntegrationEvent`	External event contract
`IIntegrationCommand` / `IIntegrationCommand<TResult>`	Cross-service command contract
`IIntegrationEventPublisher`	Publishes integration events (implemented in infra)
`IIntegrationCommandDispatcher`	Dispatches integration commands (implemented in infra)
`AssemblyScanning`	`GetLoadableTypes` — scan guard against `ReflectionTypeLoadException`

Usage

Register

// Handlers only — no pipeline behaviors:
builder.Services.AddKotoApplication(typeof(Program).Assembly);

// With behaviors (opt-in; registration order = execution order, first is outermost):
builder.Services.AddKotoApplication(
    o => o.AddLoggingBehavior().AddTransactionBehavior(),
    typeof(Program).Assembly);
builder.Services.AddKotoValidation(typeof(Program).Assembly); // ValidationBehavior from Koto.Validation
// Recommended order: Logging → Validation → Transaction.

Implement a command

public sealed record PlaceOrderCommand(Guid CustomerId, List<OrderItem> Items)
    : ICommand<OrderId>;

public sealed class PlaceOrderHandler : ICommandHandler<PlaceOrderCommand, OrderId>
{
    public async Task<Result<OrderId>> HandleAsync(PlaceOrderCommand cmd, CancellationToken ct)
    {
        // business logic
    }
}

Dispatch

var result = await _dispatcher.SendAsync(new PlaceOrderCommand(customerId, items), ct);

Pipeline behaviors

Behaviors are resolved against the concrete command/query type: an open-generic registration like ValidationBehavior<,> closes over PlaceOrderCommand at dispatch time, so IValidator<PlaceOrderCommand> is discovered. A behavior can also target a single request by implementing IPipelineBehavior<PlaceOrderCommand, Result<OrderId>>.

// Custom open-generic behavior:
builder.Services.AddKotoApplication(
    o => o.AddLoggingBehavior().AddBehavior(typeof(MyMetricsBehavior<,>)),
    typeof(Program).Assembly);

Design notes

IDomainEvent — internal; free to change; never crosses service boundaries.
IIntegrationEvent — external contract; versioned; published to Kafka via Wolverine.
IIntegrationCommand — fire-and-forget command to another service; IIntegrationCommand<TResult> expects a reply.