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# -*- mode: ruby -*-
# vi: set ft=ruby :

Vagrant.configure(2) do |config|
  config.vm.box = "ubuntu/trusty64"
  config.vm.network "private_network", ip: "192.168.33.10"
  config.vm.provision "shell", inline: <<-SHELL
    wget https://packages.erlang-solutions.com/erlang-solutions_1.0_all.deb && sudo dpkg -i erlang-solutions_1.0_all.deb
    sudo apt-get update
    sudo apt-get install -y nodejs

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Elixir tips

Editor

• Atom editor.
• atom-elixir package.

Style guide

• The Elixir style guide.

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defmodule Projections.Repo.Migrations.CreateProjectionVersions do
  use Ecto.Migration

  def change do
    create table(:projection_versions, primary_key: false) do
      add :projection_name, :text, primary_key: true
      add :last_seen_event_id, :bigint

      timestamps
    end

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# Aggregates are just collections of command functions, which emit events,
# and event handlers, which mutate state.
# In order to hold state, they should be also structs.

# There is no new() function because aggregates aren't supposed to appear
# out of the blue, they are always the result of a command.
# In this case, %OpenAccount{}.

defmodule Bank.Account do
  defstruct [:account_number, :balance]

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defp upsert_profile(multi, source, source_uuid, profile_url) do
  profile = %Profile{
    source: source,
    source_uuid: source_uuid,
    profile: profile_url,
  }

  Ecto.Multi.insert(multi, source_uuid, profile, on_conflict: [set: [profile: profile_url]], conflict_target: [:source, :source_uuid])
end

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Domain-driven design shipping example implemented using Commanded

Inspired by Peter C Marks' ddd_elixir_stage1_umbrella repo.

I've implemented the cargo event handling workflow using the approach dictated by the Commanded CQRS/ES library for Elixir.

The flow is as follows:

1. HandlingEventController web controller constructs a TrackHandling command struct from given POST params.
2. TrackHandling command is dispatched using the CommandRouter, which has configured the command to handler/aggregate mapping.

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Using Commanded Ecto projections

Example read model projections using Commanded Ecto projections where Elixir's Registry is used for pub/sub notifications of read model updates.

This alleviates the problem of async read model updates.

The command dispatcher can wait until the read model has been updated to the exact aggregate version (as returned by the dispatch command):

with {:ok, version} <- Router.dispatch(register_user, include_aggregate_version: true) do

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defmodule Example.Cart do
  use Chronik.Aggregate

  alias Example.Cart
  alias Example.DomainEvents.{CartCreated, ItemsAdded, ItemsRemoved}

  defstruct [id: nil, items: %{}]

  ## Public API

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Dealing with eventually consistent read model projections in Commanded

Example

with {:ok, version} <- Router.dispatch(command, include_aggregate_version: true),
     {:ok, projection} <- wait_for_projection_version(ExampleProjection, uuid, version) do   

  # ... safely use up-to-date read model projection at expected version
 

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defmodule Article do
  defstruct [:content, comments: []]
  
  # public commands
  
  def execute(%Article{}, %PublishArticle{content: content}) do
    %ArticlePublished{content: content}
  end
  
  def execute(%Article{}, %CommentOnArticle{} = comment) do