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Chapter.3 Controllers

sample Project would be videologue; allowing live chat over elsewhere hosted videos embbeded at it

Understanding Controllers

  • we are going to handle users; for a controller that handles users
connection |> endpoint() |> router() |> browser_pipeline() |> UserController.action()

# breaking down last part further

..connection |> UserController.index() |> UserView.render("index.html")

  • request enters via endpoint.ex; then to router.ex; then calling UserController action

  • assuming request invokes index function the View and Template constructs need be prepared

The Context

  • Phoenix Context groups function with common buziness logic purpose; like CRUD for Users can be in a single module

  • Controller exists to work with Context and translate their result into something for end-user

  • Context are unaware of Controllers

  • Business Logic Changes would just restrict to Context; Unit test business logic via Context API; integration tests focused on Contoller

Creating the Project

mix phx.new videologue

mix ecto.create

mix phx.server

A Simple Home Page

<section class="phx-hero">
  <h1><%= gettext "Welcome to %{name}!", name: "Video.logue" %></h1>
  <p>Start the videologue..</p>
</section>

Working with Contexts

shall act like Bounded Contexts from DDD

  • starting with hard-coded data for short term allowing build rapidly and test the app; later replace with full db backed Ecto repo

  • create Accounts to group user concerns together

start with file user.ex with basic struct

defmodule Videologue.Accounts.User do
  defstruct [:id, :name, :username]
end

Elixir Structs

  • Elixir Structs are special Maps with __struct__ key

  • add list_users/0, get_user/1, get_user_by/1 functions to interact with User struct at accounts.ex initiationg Accounts Context

this would let you do things like

iex(1)> Videologue.Accounts.list_users
[
  %Videologue.Accounts.User{id: "1", name: "Alice", username: "Alice InChains"},
  %Videologue.Accounts.User{id: "2", name: "Bob", username: "Bob Cat"},
  %Videologue.Accounts.User{id: "3", name: "Chad", username: "Chad Wick"}
]
iex(2)> Videologue.Accounts.get_user("2")
%Videologue.Accounts.User{id: "2", name: "Bob", username: "Bob Cat"}
iex(3)> Videologue.Accounts.get_user("@")
nil
iex(4)> Videologue.Accounts.get_user_by(name: "Alice")
%Videologue.Accounts.User{id: "1", name: "Alice", username: "Alice InChains"}

Building a Controller

  • can create all routes by resources macro; but that later

  • add UserController.index & UserController.show routes

:show, :index, :new, :create, :edit, :update, :delete actions are frequently/conventionally used

defmodule VideologueWeb.UserController do
  use VideologueWeb, :controller

  alias Videologue.Accounts

  def index(conn, _params) do
    users = Accounts.list_users()
    render(conn, "index.html", users: users)
  end
...

Coding Views

  • view is a module containing rendering functions to HTML/JSON from data

add user_view.ex with VideologueWeb.UserView.first_name/1 returning first-name for a user

  • template is a function on module; compiled from a file containing raw markup & embedded elixir

add index.html.eex with VideologueWeb.UserView.first_name/1 returning first-name for a user

  • template here shows multiline split looping with value chaining in html; alongwith link ... addition using existing Route function
  • templates are functions; Phoenix builds them using linked lists instead of traditional string concat it doesn't have to make giant string copies

this blog explains it well

uses I/O List data structure to leverage writev to minimize data copies when writing for a limited element list to use no-Copy magic

Using Helpers

  • are simple Elixir functions like link before

  • helpers are available from use VideologueWeb, :view which at lib/videologue_web.ex#view

view uses quote to inject some code into each view; one is to use Phoenix.HTML which also provides HTML safety

Showing a User

  • add VideologueWeb.UserController.show/2 with %{"id" => id} for params

  • add show.html.eex utilizing @user from Assigns

Controller UserController would infer its View name UserView; this view would look for templates at lib/videologue_web/templates/user

  • can nest templates like adding templates/user/user.html.eex & inject into show.html.eex as
<h1>User Details</h1>
<%= render "user.html", user: @user %>

  • here View is like a Module and Template its functions; each template in app becomes render(template_name, assigns)

  • utilizing it can simple respond for specific error messages in VideologueWeb.ErrorView by adding something like def render("401.html", _assigns), do: "Who are you to try this?"

  • by default error view implements template_not_found/2 callback

  • when render gets called in Controller it first renders Layout view; then renders actual template in pre-def markup

  • each template receive certain special assigns like @view_module, @view_template which gets rendered from app.html.eex

  • @conn is also available in layouts to access any other Phx helpers

Wrapping Up

chapter-04