eventric

Not production ready. API might change heavily.

eventric.js

Behavior-first application development. Runs on NodeJS and modern Browsers.

Note: eventric is currently under heavy development. The readme is outdated. It will be updated soon.

Philosophy

• Emphasize Domain-driven design, Event-driven architecture and Task-based UIs.
• Start with the Behavior of your application and go from there (BDD)
• Put the the Domain Model in the very center of your Layered Architecture (Onion / Hexagonal)
• Explicitly set boundaries for parts of your application (BoundedContexts / MicroServices)
• Separation of concerns using Commands and Queries (CQRS)
• Capture all changes to your application state as a sequence of DomainEvents (EventSourcing)
• Be reactive (Manifesto)

Getting started

npm install eventric

Important: eventric requires Promises. If you have to support older browsers use the es6-promise polyfill.

Setup Context

Having discussed the upcoming TodoApp Project with the Business-Experts and fellow Developers it got clear that we should start with a Context named Todo.

eventric = require('eventric');

todoContext = eventric.context('Todo');

Define the Event

Inside of our Todo Context things will happen which are called DomainEvents. A technique to come up with these is called EventStorming. Lets add two called TodoCreated and TodoDescriptionChanged.

todoContext.defineDomainEvents({
  TodoCreated: function(params) {},
  TodoDescriptionChanged: function(params) {
    this.description = params.description;
  }
});

Adding an Aggregate

Now we need an Aggregate which actually raises this DomainEvents.

todoContext.addAggregate('Todo', function() {
  this.create = function() {
    this.$emitDomainEvent('TodoCreated');
  }
  this.changeDescription = function(description) {
    this.$emitDomainEvent('TodoDescriptionChanged', {description: description});
  }
});

Hint: this.create is called by convention when you create an aggregate using this.$aggregate.create

Hint: this.$emitDomainEvent is dependency injected

Adding CommandHandlers

To actually work with the Context from the outside world we need CommandHandlers. Let's start by adding a simple one that will create an instance of our Todo Aggregate.

todoContext.addCommandHandlers({
  CreateTodo: function(params) {
    return this.$aggregate.create('Todo')
    .then(function (todo) {
      return todo.$save();
    });
  }
});

Hint: this.$aggregate is dependency injected

It would be nice if we could change the description of the Todo, so let's add this CommandHandler too.

todoContext.addCommandHandlers({
  ChangeTodoDescription: function(params) {
    return this.$aggregate.load('Todo', params.id)
    .then(function (todo) {
      todo.changeDescription(params.description);
      return todo.$save();
    });
  }
});

Subscribe to a DomainEvent

And last but not least we want to console.log when the description of the Todo changes.

todoContext.subscribeToDomainEvent('TodoDescriptionChanged', function(domainEvent) {
  console.log(domainEvent.payload.description);
});

Executing Commands

Initialize the Context, create a Todo and tell the Todo to change its description.

todoContext.initialize()
.then(function() {
  return todoContext.command('CreateTodo');
})
.then(function(todoId) {
  return todoContext.command('ChangeTodoDescription', {
    id: todoId,
    description: 'Do something'
  });
});

After executing the Commands the DomainEventHandler will print Do something. Your Todo Aggregate is now persisted using EventSourcing into the InMemory Store.

License

MIT

Copyright (c) 2013-2015 SixSteps Team, eFa GmbH