eventric

Not released yet. This hint will disappear with version 0.1.0.

eventric.js

Build web applications based on Domain-driven Design and Layered Architecture.

Runs on NodeJS and modern Browsers. Therefore it's easy to share code between Server and Client. Information regarding the API and more can be found in the Wiki.

Why?

It is an alternative to MVC+CRUD Frameworks where you put a lot of effort into defining your data structure and so often end up with an anemic domain model on larger projects.

How?

Basically you define queries and commands on BoundedContexts. The commands can result in series of DomainEvents consisting of properties that changed inside affected Aggregates. These DomainEvents represent the state of your domain model. DomainEvents get either persisted directly into the EventStore or send over a RemoteService first. The RemoteService can also be used to execute queries and commands remotely. This makes eventric.js really useful for distributed applications.

Philosophy

• Emphasize Domain-driven design, Event-driven architecture and Task-based UIs.
• 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 events (EventSourcing / DomainEvents)

Quick Start

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

Setup BoundedContext

Hint: You should npm install eventric and npm install eventric-store-mongodb first.

Let's get right into it and create our BoundedContext

eventric = require('eventric');

collaborationContext = eventric.boundedContext();

Adding Aggregate

Now that we created the collaborationContext let's add our Todo Aggregate, consisting of a simple changeDescription method.

collaborationContext.addAggregate('Todo', {
  changeDescription: function(description) {
    this.description = description;
  }
});

Hint: values assigned to this. are automatically part of the generated DomainEvent

Adding Commands

To actually work with the BoundedContext from the outside world we need commands and queries. Let's start by adding a simple command that will create an instance of our Todo Aggregate.

collaborationContext.addCommand('createTodo', function(params, callback) {
  this.aggregate.create('Todo', callback);
});

Hint: this.aggregate is dependency injected

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

collaborationContext.addCommand('changeTodoDescription', function(params, callback) {
  this.aggregate.command('Todo', params.id, 'changeDescription', params.description, callback);
});

Hint: If successful this will trigger a Todo:changeDescription DomainEvent

Adding Query

And last but not least we want the ability to query for a Todo by its id.

collaborationContext.addQuery('getTodoById', function(params, callback) {
  this.repository('Todo').findById(params.id, callback);
});

Hint: this.repository is dependency injected

Executing Commands and Queries

Initialize the collaborationContext, create a Todo, change the description of it and finally query the description again.

collaborationContext.initialize(function() {
  collaborationContext.command({
    name: 'createTodo'
  },
  function(err, todoId) {
    collaborationContext.command({
      name: 'changeTodoDescription',
      params: {
        id: todoId,
        description: 'Do something'
      }
    },
    function(err, status) {
      collaborationContext.query({
        name: 'getTodoById',
        params: {
          id: todoId
        }
      },
      function(err, readTodo) {
          console.log(readTodo.description);
      })
    });
  });

});

eventric will implement promises to avoid such a "Pyramid of Doom" in the future.

This will output Do something. Your Todo Aggregate is now persisted using EventSourcing.

Congratulations, you have successfully applied DDD (tactical+technical) and CQRS! :)

Running Tests

To execute all (client+server) tests, use:

gulp spec

You can watch for file-changes with

NODE_ENV=workstation gulp watch

License

MIT

Copyright (c) 2013-2014 SixSteps Team, eFa GmbH