Installation and Usage

git clone [email protected]:fborello-lambda/phoenix_in_action.git
cd phoenix_in_action
mix deps.get
mix phx.server

Elixir

spawn(<function>) → runs the function asynchronously.

scope of anonymous functions, variables after the function can be accessed (closures). AVOID

Parenthesis can be omitted when calling named functions:

IO.puts("with parens") IO.puts "no parens"

Modules: Module.<function>(parameters) They use CamelCase and module’s filenames use snake_case.

Function arities → number of arguments a function receives.

Capture operator

Creating an anonymous function:

iex(5)> mult = &(&1 * &2)
> &:erlang.*/2
iex(6)> mult.(10,5)
> 50

Control Flow with Functions:

defmodule Compare do
  def greater(left, right) do
    check(left >= right, left, right)
  end

  defp check(true, left, _), do: left
  defp check(false, _, right), do: right
end

Elixir’s compiler needs the require directive to use the module in the compilation phase when using macros.

Tail Recursive Functions → limits the amount of memory used (sometimes the memory usage is excessive if recursion is used).

Some recursive functions don’t have boundaries. “Timers” or “Max_depth” can be used, max_depth stands for the amount of recursive function.

An anonymous recursive function can be created with a named function and the & (capture operator) to capture de function’s reference.

Comprehensions:

iex(32)> for x <- ["a", "b", "c"], do: String.upcase(x)
> ["A", "B", "C"]

Elixir has Structs and Polymorphic functions with “Protocols”.

Erlang’s Dialyzer tool → analyzes code → “dialyxir” module for Elixir

• Key Aspects of elixir:
  • Persistent Data Structures → Immutability
  • Preemptive scheduler
  • Testing: properties to test for your code and writing good generators for the data over which you want to test.
• Enum Cheatsheet

Phoenix

Phoenix in Action Repo w v1.7.10

Phoenix LiveView simple project

Phoenix Playlist → Useful

Phoenix in Action comments

Set up Postgres docker container:

docker run \
	--name phx_db \
	-e POSTGRES_USER=phx_db \
	-e POSTGRES_PASSWORD=phx_test \
	-p 5432:5432 \
	-d postgres 

Inside /phx_app/config/dev.exs if using a standalone phx-app change:

# Configure your database
config :demo, Demo.Repo,
  username: "phx_db",   #POSTGRES_USER
  password: "phx_test", #POSTGRES_PASSWORD
  hostname: "localhost",
  database: "demo_dev",
  stacktrace: true,
  show_sensitive_data_on_connection_error: true,
  pool_size: 10

(Only used when developing). Now mix ecto.create can be used to create de Postgres database.

Phoenix Structure // How it works?

flowchart TD

	subgraph PhoenixProcess
			direction TB
			subgraph Router
					direction TB
				r1(["'pipelines'"]) --> r2(["Searches the route by  'scope'"])
			end
			e1(["Using 'plugs'"]) --> Endpoint --> Router --> ControllerProcess
			
			subgraph ControllerProcess
				direction TB
				Controller --> index
				Controller --> new
				Controller --> create
				Controller --> show
				Controller --> edit
				Controller --> delete
				Controller --> update
			end
			
			subgraph View
					direction TB
				v1(["'Render Function'"]) 
			end

			DB[("DataBase")] <-- ConnectsTo --> ControllerProcess --> View --> Templates

			

			
	end				
	WebRequest --> PhoenixProcess --> SendRequest

Loading

If the the Phoenix App is named demo → demo_web is the dir in which all the components, controllers, and routes are specified.

/demo/lib
├── demo
│   ├── application.ex
│   ├── mailer.ex
│   └── repo.ex
├── demo.ex
├── demo_web
│   ├── components
│   ├── controllers
│   ├── endpoint.ex
│   ├── gettext.ex
│   ├── router.ex
│   └── telemetry.ex
└── demo_web.ex

pipelines group plugs

If a scope is defined inrouter.ex, such as the following one:

#[...]
scope "/demo", DemoWeb do
    pipe_through(:browser)

    get("/", TestController, :index)
  end
#[...]

means that the route “/demo” will “open” the TestController controller defined inside /demo_web/controllers. Now, following the guidelines another module to specify the path to the html files should be created /demo_web/controllers/test_html.ex inside it:

defmodule AuctionWeb.TestHTML do
  use AuctionWeb, :html

  embed_templates "test_html/*"
end

The embed_templates function is trying to bind the htmls inside the path /demo_web/controllers/test_html to the controller. The html.heex templates have to be placed in that dir.

Phoenix in Action

Phoenix in action chapter6 → {Phoenix.PubSub, name: AuctionWeb.PubSub} aboveAuctionWeb.Endpoint, in <umbrella>/apps/auction_web/lib/auction_web/application.ex . This handles the pubsub error.

Phoenix 1.7.x Routing → Useful, links can be done like this:

<%= for item <- @items do %>
    <li>
      <strong class="bg-brand/5 text-[0.8125rem] ml-3 rounded-full px-2 font-medium leading-6 text-orange-400	">
        <.link href={~p"/items/#{item.id}"}><%= item.title %></.link>
      </strong>
      - <%= item.description %>
    </li>
<% end %>

/items is the route specified inside router.ex

scope "/", AuctionWeb do
    pipe_through :browser

    get "/", PageController, :home
    resources "/items", ItemController, only: [:index, :show, :create, :new]
  end

And controllers/item_controller.ex

defmodule AuctionWeb.ItemController do
  use AuctionWeb, :controller

  def index(conn, _params) do
    # The home page is often custom made,
    # so skip the default app layout.
    render(conn, :test, layout: false)
  end

  def show(conn, %{"id" => id}) do
    # The home page is often custom made,
    # so skip the default app layout.
    item = Auction.get_item(id)
    render(conn, :show, item: items, layout: false)
  end
end

And the views are defined inside controllers/item_html.ex

defmodule AuctionWeb.ItemHTML do
  use AuctionWeb, :html

  embed_templates "item_html/*"
end

The controller calls the function render/3 with the Plug.conn, the html template specified as an atom. :test → refers to →item_html/test.html.heex. A variable can be passed to the template, for example, the function show() calls render(conn, :show, item: items). , now the variable “item” can be accessed inside the template == :show == show.html.heex as follows: @items. The first line showing how to code links,<%= for item <- @items do %>, demonstrates how to use the variable passes to the template.

Creating a form

I’m going to call the “controller” the controller/items_controller.ex file and the “view” will be the page_html/:atom.html.heex" . Using LiveView is maybe easier and gives you more possibilities, but if only HTML is wanted we can do the following, according to Phoenix’s Docs:

Phoenix Docs

Inside the view:

# [...]
<.form for={@form} action={~p"/items"}>
  <.input field={@form[:title]} />
	<.input
    type="datetime-local"
    value="2024-01-24T19:30"
    min="2024-01-24T00:00"
    max="2024-06-24T00:00"
    field={@form[:ends_at]}
  /> # <- input datetime with calendar gui
	<button>Save</button>
</.form>
# [...]

Inside the controller:

# [...]
use AuctionWeb, :live_view # important, makes the function "to_form()" usable

def new(conn, _params) do
	item = Auction.new_item()
	render(conn, :new, form: to_form(item), layout: false)
end
# [...]

And Auction.new_item() returns an Ecto.Changeset:

# [...]
import Ecto.Changeset

  def changeset(item, params \\ %{}) do
    item
    |> cast(params, [:title, :description, :ends_at])
    |> validate_required(:title)
    |> validate_length(:title, min: 3, max: 200)
    |> validate_length(:description, min: 3, max: 200)
    |> validate_change(:ends_at, &validate_date/2)
  end
# [...]

Take into account that \items should have “RESTful” routes, those where defined inside router.ex:

# [...]
resources "/items", ItemController, only: [:index, :show, :create, :new]
# [...]

Easy redirection

Phoenix Docs

If a form has been created, the controller will be “using” the module :liveview and :controller, to specify the redirect function from the controller module the following can be done:

# [...]
def show(conn, %{"id" => id}) do
    item = Auction.get_item(id)
    render(conn, :show, item: item, layout: false)
  end

  def new(conn, _params) do
    item = Auction.new_item()
    render(conn, :new, form: to_form(item), layout: false)
  end

  def create(conn, %{"item" => item_params}) do
    {:ok, item} = Auction.insert_item(item_params)
    Phoenix.Controller.redirect(conn, to: ~p"/items/#{item.id}") # <- Redirection
  end
# [...]

The “sigil”p == ~p makes this task easy. Here, in this module, we have the route items/new which “triggers” the new() function, whose view has the form previously defined, the form redirects to ~p"/items" with a POST request, this triggers the create() function. Finally, a redirection is performed to ~p"/items/#{item.id}", this route triggers the show() function. All this “operation” is possible because RESTful paths are defined in router.ex.

Handle Errors with the case statement

This expression is really useful. If the insertion is made without errors, based on the Ecto.Changeset, it redirects to the show() function, else it redirects again to the new() function.

def create(conn, %{"item" => item_params}) do
  case Auction.insert_item(item_params) do
    {:ok, item} -> Phoenix.Controller.redirect(conn, to: ~p"/items/#{item.id}")
    {:error, item} 
								-> 
		conn
        |> Phoenix.Controller.put_flash(:error, "Try again") # <- inserts a flash msg
        |> Phoenix.Controller.redirect(to: ~p"/items/new")
  end
 end

Inside the view:

Phoenix Docs

#[...]
<.flash_group flash={@flash} />
#[...]

How to edit? Similar to new and create but with edit and update

→ Note: Auction.edit_item() has to be defined in the non-web app:

def edit_item(id) do
  get_item(id)
  |> Item.changeset()
end

Create a new html → edit.html.heex (the view) and copy to it the new.html.heex contents. Now, inside the controller:

def edit(conn, %{"id" => id}) do
    item = Auction.edit_item(id)
    render(conn, :edit, form: to_form(item), id: id, layout: false) # <- the id is passed
  end

  def update(conn, %{"id" => id, "item" => item_params}) do
    item = Auction.get_item(id)

    case Auction.update_item(item, item_params) do
      {:ok, item} ->
        Phoenix.Controller.redirect(conn, to: ~p"/items/#{item.id}")

      {:error, item} ->
        conn
        |> Phoenix.Controller.put_flash(:error, "Try again")
        |> Phoenix.Controller.redirect(to: ~p"/items/edit/#{item.id}")
    end
  end

Look, the id is passed to the view, inside the view the following can be done:

<.form for={@form} action={~p"/items/#{@id}"} method="put"> # <- only this line is modified
																														# compared to new.html.heex
	<.input type="text" field={@form[:title]} />
	<.input type="text" field={@form[:description]} />
	<.input
	  type="datetime-local"
	  value="2024-01-24T19:30"
	  min="2024-01-24T00:00"
	  max="2024-06-24T00:00"
	  field={@form[:ends_at]}
/>

Phoenix seems smart enough to detect that the form was generated with an “edit” trigger, so the form will generate automatically a PUT response, but it can be explicitly defined with the “method” keyword.

Phoenix in Action Summary of chapter 9

Good workflow

• Add the routes
• Create the Controller and Add the functions
• Create the html template (Views)

Recap

• A RESTful resource contains actions for index, show, new, create, edit, update and delete.
• Each controller accepts two parameters, a Plug.Conn struct and the parameters from the user request.

→ Note: Ecto.Schema virtual field for non-hashed passwords. Multiple changesets help to provide more security limiting the access to the password.

→ Plugs are powerful to handle sessions.

Chapter 10

I couldn’t make it work the following: delete "/logout", SessionController, :delete.. I changed it to handle “GET” requests, which are triggered with a simple form with a button, whose action is "login"

Chapter 11

Define global functions embedded in the htmls, inside auction_web/lib/auction_web.ex:

defp html_helpers do
  quote do
		#[...]
    import AuctionWeb.GlobalHelpers
  end
end

And the module AuctionWeb.GlobalHelpers can be defined inside a file named auction_web/lib/global_helpers.ex. The functions defined inside the module can be accesed directly inside the html.

<%= "#{integer_to_currency(bid.amount)}" %>

In the example above, integer_to_currency() is a function from the GlobalHelpers module.

Code an API on top of the HTML web_app

Phoenix Docs

Create a new folder named api and add the following files → /controllers/api/item_controller.ex and /controllers/api/item_json.ex

Inside item_controller.ex:

defmodule AuctionWeb.Api.ItemController do
  use AuctionWeb, :controller

  def index(conn, _params) do
    items = Auction.list_items()
    render(conn, :index, items: items)
  end
end

Inside item_json.ex:

defmodule AuctionWeb.Api.ItemJSON do
  alias Auction.Item

  def index(%{items: items}) do
    %{data: for(item <- items, do: data(item))}
  end

  defp data(%Item{} = item) do
    %{
      id: item.id,
      title: item.title,
      descr: item.description,
      ends_at: item.ends_at
    }
  end
end

The index function inside the item_json.ex is called by the controller automatically whenever the render function is called with the :index atom.

Finally, in router.ex uncomment the ”/api” scope and add the following:

scope "/api", AuctionWeb do
  pipe_through :api

  resources "/items", Api.ItemController, only: [:index, :show]
end