Where can I put my Plugs and then use them from different controllers in my Phoenix app?

Question

I'm creating my first Elixir-Phoenix app. I've written a few plugs that I want to use in multiple controllers, right now there is a lot of code duplication since the Plug code is being repeated in all of my controllers.

My question is, is there a file where I can put all of my Plugs and then access and use them from different controllers?

# somefile to define my plugs

defp load_subject(conn, _) do
    subject = Subject |> Repo.get conn.params["subject_id"]

    assign(conn, :subject, subject)
end

defp load_topic(conn, _) do
    topic = Topic |> Repo.get conn.params["topic_id"]

    conn |> assign :topic, topic
end

Then use them in my controllers:

# First Controller
defmodule MyApp.FirstController do
    use MyApp.Web, :controller

    plug :load_subject
    plug :load_topic
    plug :action

    def some_action(conn, _) do
        # do something
    end

    def another_action(conn, _) do
        # do some other thing
    end
end

# Second Controller
defmodule MyApp.SecondController do
    use MyApp.Web, :controller

    plug :load_subject
    plug :load_topic
    plug :action

    def lame_action(conn, _) do
        # do something
    end

    def cool_action(conn, _) do
        # do some other thing
    end
end

Answer 1

You can define the plugs in any module as public functions:

defmodule MyApp.Loaders do
  import Plug.Conn

  def load_subject(conn, _) do
    subject = Subject |> Repo.get conn.params["subject_id"]
    assign(conn, :subject, subject)
  end

  def load_topic(conn, _) do
    topic = Topic |> Repo.get conn.params["topic_id"]
    conn |> assign :topic, topic
  end
end

Now you can import it in your controllers and use the plugs:

defmodule MyApp.Controller do
  use MyApp.Web, :controller
  import MyApp.Loaders

  plug :load_subject
  plug :load_topic
  plug :action

  ...
end

Alternatively, you can also create a pipeline in your router:

import MyApp.Loaders

pipeline :with_subject_and_topic do
  plug :load_subject
  plug :load_topic
end

And then pipe_through it in the relevant scopes.