nicholasjhenry

Event sourcing: making it functional

nicholasjhenry

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

nicholasjhenry

GraphQL Schema Language Cheat Sheet

The definitive guide to express your GraphQL schema succinctly

A port of a cheat sheet authored by Hafiz Ismail.

What does it look like?

defmodule MyApp.Schema do
 use Absinthe.Schema

nicholasjhenry

defmodule Example.Server do
  use GenServer

  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, :ok, opts)
  end

  def init(state) do
    Process.flag(:trap_exit, true) # must trap exit for terminate call back to work
    IO.inspect "Starting server..."

nicholasjhenry

// https://groups.google.com/d/msg/growing-object-oriented-software/mCjbhcRAGDs/P7pkf62XBgAJ

interface UserLookup {
    fun findByName(name: String): User
}

interface PermissionDecision {
    fun rejected(user: User)
    fun allowed(user: User)
}

nicholasjhenry

# http://slack.elixirhq.com/absinthe-graphql/2016-08-16/

defp flatten_errors(changeset = %Ecto.Changeset{}) do
  Ecto.Changeset.traverse_errors(changeset, fn {error, _interpolates} -> error end)
  |> Enum.map(&flatten_errors/1)
  |> List.flatten
end
defp flatten_errors(errors) when is_map(errors),
  do: Enum.map(errors, &flatten_errors/1)
defp flatten_errors({key, errors}) when is_list(errors),

nicholasjhenry

defmodule MyApp.Subscriber do
  use GenServer

  def start_link(channel) do
    GenServer.start_link(__MODULE__, channel)
  end

  def init(channel) do
    pid = self
    ref = MyApp.Endpoint.subscribe(pid, channel)

nicholasjhenry

defmodule Foo do
  def call(x) do
    IO.puts x
  end
  def bar(x, y) do
    IO.puts x
    IO.puts y
  end
end

nicholasjhenry

class DraftNewLetter
  def self.build(current_user)
    @create_letter = CreateLetter.new
    @authorize = Authorize.new(current_user, @create_letter)
    @error_handler = ActiveRecordErrorHandler.new(@authorize)    
    @assign_automatic_ccs = AssignAutomaticCCs.new(@create_letter)
    @transaction = Transaction.new(@assign_automatic_ccs)
  end
end

nicholasjhenry

params = %{
  "title" => "Test List",
  "todo_items" => %{
    "0" => %{"body" => "change to-do A", "id" => "1"},
    "1" => %{"body" => "change to-do B", "id" => "2"}
  }
}

changeset = %Ecto.Changeset{
  action: nil,