Update the RedirectionController.

lib/link_shortener/links/links.ex

@@ -23,6 +23,14 @@ defmodule LinkShortener.Links do
     Repo.get!(Link, id)
   end
 
+  def get_one_by!(attrs) do
+    Repo.get_by!(Link, attrs)
+  end
+
+  def get_one_by_shorten!(shorten) do
+    get_one_by!(%{shorten: shorten})
+  end
+
   def get_one_by(attrs) do
     Repo.get_by(Link, attrs)
   end

lib/link_shortener_web/controllers/redirection_controller.ex

@@ -0,0 +1,10 @@
+defmodule LinkShortenerWeb.RedirectionController do
+  use LinkShortenerWeb, :controller
+
+  alias LinkShortener.Links
+
+  def show(conn, %{"shorten" => shorten}) do
+    %{url: url} = Links.get_one_by_shorten!(shorten)
+    redirect(conn, external: url)
+  end
+end

lib/link_shortener_web/router.ex

@@ -18,6 +18,7 @@ defmodule LinkShortenerWeb.Router do
     pipe_through :browser
 
     get "/", PageController, :home
+    get "/u/:shorten", RedirectionController, :show
   end
 
   scope "/api", LinkShortenerWeb do

test/link_shortener_web/controllers/redirection_controller_test.ex

@@ -0,0 +1,30 @@
+defmodule LinkShortenerWeb.RedirectionControllerTest do
+  use LinkShortenerWeb.ConnCase
+
+  import LinkShortener.LinksFixtures
+
+  alias LinkShortener.Links.Link
+  alias LinkShortener.Links
+
+  @invalid_shorten "invalid_shorten"
+
+  describe "redirection via a link" do
+    setup [:create_link]
+
+    test "redirected via the shorten", %{conn: conn, link: %Link{shorten: shorten} = link} do
+      conn = get(conn, ~p"/u/#{shorten}")
+      assert response(conn, 302)
+    end
+
+    test "no redirection if a shorten is not found", %{conn: conn, link: link} do
+      assert_error_sent 404, fn ->
+	conn = get(conn, ~p"/u/#{@invalid_shorten}")
+      end
+    end
+  end
+
+  defp create_link(_) do
+    link = link_fixture()
+    %{link: link}
+  end
+end