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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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#!/bin/bash
(while(true); do  \
(mysql -e 'show innodb status \G' | grep undo\ log\ entries ; sleep 1 ;  \
mysql -e 'show innodb status \G' | grep undo\ log\ entries ) |    \
egrep '[0-9][0-9][0-9][0-9]' |awk '{print $10;}' ; done ) | \
perl -e '$t = ROWS_IN_TABLE; while(1) { \
$n ++; $nn; $a = <>; $b = <>; $nn += ($b-$a); \
printf "Rate: %d, avg: %d, %0.3f%% complete, done in %d sec\n", \
$b-$a, $nn/$n, ($b/$t)*100, ($t-$b)/($nn/$n); }';

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# config/config.exs
use Mix.Config

config :my_app, consistency: :eventual

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defmodule Swarm.Distribution.LimitedRing do
  @moduledoc false
  use Swarm.Distribution.Strategy

  @app_nodes [
    :"myapp1@127.0.0.1", 
    :"myapp2@127.0.0.1", 
    :"myapp3@127.0.0.1"
  ]
  

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# test/support/data_case.ex
defmodule MyApp.DataCase do
  use ExUnit.CaseTemplate

  using do
    quote do
      import Ecto
      import Ecto.Changeset
      import Ecto.Query
      import Commanded.Assertions.EventAssertions

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# This demonstrates that, when using async/await, a crash in the task will crash the caller
defmodule Tasker do
  def good(message) do
    IO.puts message
  end

  def bad(message) do
    IO.puts message
    raise "I'm BAD!"
  end

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defmodule Withdraw do
  defstruct [:account_number, :amount]
end

defmodule Withdrawn do
  defstruct [:account_number, :amount]
end

defmodule WithdrawalRejected do
  defstruct [:account_number, :amount]

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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

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# Elixir v1.0
defmodule Rules do
  defmacro __using__(_) do
    quote do
      import unquote(__MODULE__)
      @before_compile unquote(__MODULE__)
      @rules []
    end
  end

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defmodule MyApp.DataCase do
  use ExUnit.CaseTemplate

  using do
    quote do
      import Commanded.Assertions.EventAssertions
    end
  end

  setup do