Super-short example
So how does it actually look when writing an application with Revo?
These few following paragraphs show how could one design super-simple application that can save tasks using event-sourced aggregates and then query them back from a RDBMS.
A little-bit more complete application based on this code, along with some walkthrough, can be found in the Task list app example.
Event
The event that happens when changing a task's name.
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public class TodoRenamedEvent : DomainAggregateEvent
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{
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public TodoRenamedEvent(string name)
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{
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Name = name;
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}
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​
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public string Name { get; }
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}
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Aggregate
The task aggregate root.
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public class Todo : EventSourcedAggregateRoot
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{
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public Todo(Guid id, string name) : base(id)
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{
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Rename(name);
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}
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protectedTodo(Guid id) : base(id)
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{
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}
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​
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public string Name { get; private set; }
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​
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public void Rename(string name)
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{
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if (!Name != name)
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{
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Publish(new TodoRenamedEvent(name));
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}
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}
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private void Apply(TodoRenamedEvent ev)
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{
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Name = ev.Name;
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}
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}
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Command and command handler
Command to save a new task.
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public class CreateTodoCommand : ICommand
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{
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public CreateTodoCommand(string name)
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{
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Name = name;
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}
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​
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[Required]
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public string Name { get; }
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}
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public class TodoCommandHandler : ICommandHandler<CreateTodoCommand>
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{
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private readonly IRepository repository;
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public TodoCommandHandler(IRepository repository)
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{
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this.repository = repository;
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}
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​
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public Task HandleAsync(CreateTodoCommand command, CancellationToken cancellationToken)
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{
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var todo = new Todo(command.Id);
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todo.Rename(command.Name);
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repository.Add(todoList);
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return Task.CompletedTask;
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}
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}
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Read model and projection
Read model and a projection for the event-sourced aggregate.
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public class TodoReadModel : EntityReadModel
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{
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public string Name { get; set; }
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}
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public class TodoListReadModelProjector : EFCoreEntityEventToPocoProjector<Todo, TodoReadModel>
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{
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public TodoListReadModelProjector(IEFCoreCrudRepository repository) : base(repository)
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{
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}
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​
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private void Apply(IEventMessage<TodoRenamedEvent> ev)
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{
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Target.Name = ev.Event.Name;
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}
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}
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Query and query handler
Query to read the tasks back from a RDBMS.
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public class GetTodosQuery : IQuery<IQueryable<TodoReadModel>>
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{
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}
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public class TaskQueryHandler : IQueryHandler<GetTodoQuery, IQueryable<TodoReadModel>>
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{
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private readonly IReadRepository readRepository;
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​
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public TaskListQueryHandler(IReadRepository readRepository)
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{
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this.readRepository = readRepository;
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}
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​
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public Task<IQueryable<TodoReadModel>> HandleAsync(GetTodoListsQuery query, CancellationToken cancellationToken)
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{
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return Task.FromResult(readRepository
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.FindAll<TodoListReadModel>());
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}
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}
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ASP.NET Core controller
Or just any arbitrary endpoint from where to send the command and queries from. :)
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[Route("todos")]
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public class TodoController : CommandApiController
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{
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[HttpGet("")]
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public Task<IQueryable<TodoReadModel>> Get()
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{
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return CommandBus.SendAsync(new GetTodosQuery());
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}
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​
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[HttpPost("")]
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public Task Post([FromBody] CreateTodoDto payload)
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{
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return CommandBus.SendAsync(new CreateTodoCommand(payload.Name));
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}
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public class CreateTodoDto
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{
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public string Name { get; set; }
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}
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}
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Finish!
Now you are ready save the TO-DOs to an event store and read them from regular RDBMS read models.
Last modified 2yr ago