EventSourcery::Rails

Short description and motivation.

Usage

Commands

EventSourcery::Rails adds an optional base class for commands to enforce instantiating commands with an aggregate_id and required parameters as keyword arguments. Defined attributes are available with an attr_reader.

class AddUser < EventSourcery::Rails::Command
  attributes :name, :email
end

AddUser.new # => raises ArgumentError.new("missing keywords: aggregate_id, name, email")

command = AddUser.new(aggregate_id: 'aggregate-id',
                      name: 'name',
                      email: 'email')
command.aggregate_id # => "aggregate-id"
command.name # => "name"
command.email # => "email"

Command Handlers

You can also optionally include EventSourcery::Rails::CommandHandler to use use a callback DSL for binding commands. This DSL allows your application code to use all command handlers with #call.

Todo

• [ ] Consider switching to a base class with common initializer and with_aggregate
• [ ] Introduce API for invoking all known command handlers with an array of commands.

class UserCommandHandler
  include EventSourcery::Rails::CommandHandler

  attr_reader :repository

  def initialize(repository: EventSourceryRails.repository)
    @repository = repository
  end

  on AddUser do |command|
    aggregate = repository.load(UserAggregate, aggregate_id)
    aggregate.add(name: command.name,
                  email: command.email)
    repository.save(aggregate)
  end

  on UpdateUserEmail do |command|
    aggregate = repository.load(UserAggregate, aggregate_id)
    aggregate.update_email(email: command.email)
    repository.save(aggregate)
  end
end

Installation

Add the following line to your Gemfile.

gem 'event_sourcery'
gem 'event_sourcery-postgres'
gem 'event_sourcery-rails'

Then run bundle install

Next, your need to run the generator:

$ rails generate event_sourcery_rails:install

At this point you will have an initializer to configure EventSourcery and the following Rake tasks.

$ rails event_sourcery:db:migrate # create the event sourcery schema
$ rails event_sourcery:processors:setup # create projector schemas
$ rails event_sourcery:processors:reset # drop and recreate projector schemas and data
$ rails event_sourcery:processors:run # start event stream processors

Typically you'll have the following in your Procfile.

web: rails server
processors: rails event_sourcery:processors:run

Contributing

Please submit issues and pull requests for bugs, features or ideas.

License

The gem is available as open source under the terms of the MIT License.