Nagare 0.6.4

Nagare 流れ

Event sourcing for .NET — flow in, truth out.

Events are the natural language of change. Something happened. Then something else. The stream moves forward, never backward, and the truth is always the whole story.

Nagare is an event sourcing framework for .NET that gets out of your way. Define what your domain means, and let the framework carry the rest.

public class BookAggregate : Aggregate<BookCommand, BookEvent, BookState>
{
    private readonly EventHandlers<BookEvent, BookState> _events =
        new EventHandlersBuilder<BookEvent, BookState>()
            .On<BookAdded>((state, e) =>
                state with { Exists = true, Title = e.Title })
            .On<BookBorrowed>((state, e) =>
                state with { IsBorrowed = true, BorrowerId = e.BorrowerId })
            .Build();

    private readonly CommandHandlers<BookCommand, BookEvent, BookState> _commands =
        new CommandHandlersBuilder<BookCommand, BookEvent, BookState>()
            .On<AddBook>((state, cmd) =>
                state.Exists
                    ? Then.Reject("Book already exists")
                    : Then.Persist(new BookAdded(cmd.Title, cmd.Author, cmd.Isbn)))
            .On<BorrowBook>((state, cmd) =>
                !state.Exists      ? Then.Reject("Book does not exist")
                : state.IsBorrowed ? Then.Reject("Book is already borrowed")
                : Then.Persist(new BookBorrowed(cmd.BorrowerId, DateTimeOffset.UtcNow)))
            .Build();

    protected override EventHandlers<BookEvent, BookState> RegisterEventHandlers() => _events;

    protected override CommandHandlers<BookCommand, BookEvent, BookState> RegisterCommandHandlers() => _commands;
}

Commands say what you want. Events say what happened. State is what's true right now. That's it.

Test like you think

harness
    .Given(new BookAdded("Dune", "Herbert", "978-0441172719"))
    .When(new BorrowBook("user-42"))
    .ThenAccepted()
    .ThenExpect<BookBorrowed>(e => e.BorrowerId == "user-42");

harness
    .Given(new BookAdded(...), new BookBorrowed(...))
    .When(new BorrowBook("user-99"))
    .ThenRejected("already borrowed");

No database. No DI container. Just the domain, speaking for itself.

Packages

Package	NuGet	Purpose
Nagare		Core — aggregates, events, projections, subscriptions
Nagare.SqlServer		SQL Server stores
Nagare.Sqlite		SQLite stores
Nagare.PostgreSql		PostgreSQL stores
Nagare.MySql		MySQL stores
Nagare.Messaging		Pub/sub messaging abstractions
Nagare.Messaging.Kafka		Kafka implementation
Nagare.Testing		Given-When-Then harness, Eventually for projection polling

Claude Code plugin

Nagare ships a Claude Code plugin with skills for aggregate design, event naming, projections, testing, and store adapters.

# Add the marketplace
/plugin marketplace add gideondk/nagare

# Install the plugin
/plugin install nagare@gideondk-nagare

# Reload to activate
/reload-plugins

Get started

builder.Services.AddNagare();
builder.Services.AddAggregate<BookAggregate, BookCommand, BookEvent, BookState>();

See samples/Nagare.Samples.Library for a complete example, or read the full documentation.

Nagare (流れ) — the flow of water, the passage of time, the course of events.