Elixir的Library与OTP Application的关系

所有的library必须是独立的OTP application.

defp deps do
   [{:phoenix, "~> 1.2.1"},
    {:phoenix_pubsub, "~> 1.0"},
    {:phoenix_ecto, "~> 3.0"},
    {:postgrex, ">= 0.0.0"},
    {:phoenix_html, "~> 2.6"},
    {:phoenix_live_reload, "~> 1.0", only: :dev},
    {:gettext, "~> 0.11"},
    {:comeonin, "~> 2.5"},
    {:guardian, "~> 0.14"},
    {:cowboy, "~> 1.0"}]
 end

application的依赖写在dpes中，如果该依赖只存在编译的时候，那往往就足够了，如果运行时需要此依赖，则必须在 application 函数中列出。

def application do
   [mod: {Til, []},
    applications: [:phoenix, :phoenix_pubsub, :phoenix_html, :cowboy, :logger, :gettext,
                   :phoenix_ecto, :postgrex, :comeonin]]
 end

application 函数中， mod 是一个callback。这个callback需要我们在指定的module中给出实现。

defmodule Til do
  use Application

  # See https://elixir-lang.org/docs/stable/elixir/Application.html
  # for more information on OTP Applications
  def start(_type, _args) do
    import Supervisor.Spec

    # Define workers and child supervisors to be supervised
    children = [
      # Start the Ecto repository
      supervisor(Til.Repo, []),
      # Start the endpoint when the application starts
      supervisor(Til.Endpoint, []),
      # Start your own worker by calling: Til.Worker.start_link(arg1, arg2, arg3)
      # worker(Til.Worker, [arg1, arg2, arg3]),
    ]

    # See https://elixir-lang.org/docs/stable/elixir/Supervisor.html
    # for other strategies and supported options
    opts = [strategy: :one_for_one, name: Til.Supervisor]
    Supervisor.start_link(children, opts)
  end

  # Tell Phoenix to update the endpoint configuration
  # whenever the application is updated.
  def config_change(changed, _new, removed) do
    Til.Endpoint.config_change(changed, removed)
    :ok
  end
end

这里主要就是建立本应用的supervisor tree。