A five-minute walk-through of the three message kinds Memoria dispatches: commands, queries, and notifications. Every handler returns a Result so failures travel through types, not exceptions.
If you haven’t already: install the Memoria package.
In Program.cs (or wherever you build your IServiceCollection):
services.AddMemoria(typeof(Program));
That single call scans the supplied assembly for command, query, and notification handlers and registers them. Pass one type per assembly that contains handlers.
For the full configuration surface, see Configuration: Memoria Core.
A command is a write operation handled by exactly one handler.
public class CreateProduct : ICommand
{
public string Name { get; init; } = string.Empty;
}
public class CreateProductHandler : ICommandHandler<CreateProduct>
{
private readonly IProductService _products;
public CreateProductHandler(IProductService products) => _products = products;
public async Task<Result> Handle(CreateProduct command)
{
await _products.Create(command.Name);
return Result.Ok();
}
}
// Anywhere you have IDispatcher injected:
var result = await dispatcher.Send(new CreateProduct { Name = "Espresso" });
Commands can return a value by implementing ICommand<TResponse> and ICommandHandler<TCommand, TResponse>. Beyond the happy path, see the guides for validating commands, running command sequences, using custom handlers, and publishing notifications and messages on success.
A query is a read operation handled by exactly one handler.
public class GetProduct : IQuery<Product>
{
public int Id { get; init; }
}
public class GetProductHandler : IQueryHandler<GetProduct, Product>
{
private readonly MyDbContext _db;
public GetProductHandler(MyDbContext db) => _db = db;
public async Task<Result<Product>> Handle(GetProduct query)
{
var product = await _db.Products.FindAsync(query.Id);
return product is null
? Result<Product>.Fail("Not found")
: Result<Product>.Ok(product);
}
}
var result = await dispatcher.Get(new GetProduct { Id = 123 });
Need automatic caching? See Cache queries.
A notification is a fan-out message. Any number of handlers can subscribe to the same notification type.
public class ProductCreated : INotification
{
public int Id { get; init; }
}
public class SendWelcomeEmail : INotificationHandler<ProductCreated>
{
public Task<Result> Handle(ProductCreated notification)
{
// …send an email
return Task.FromResult(Result.Ok());
}
}
public class IndexInSearch : INotificationHandler<ProductCreated>
{
public Task<Result> Handle(ProductCreated notification)
{
// …push to search index
return Task.FromResult(Result.Ok());
}
}
await dispatcher.Publish(new ProductCreated { Id = 123 });
The dispatcher invokes every registered handler and returns the list of their results. Decide what “partial success” means for your domain.