What is the use of hello_view.ex in Phoenix - phoenix-framework

Question

I was reading the 'Programming Phoenix' book to create my first MVC simple routing project. In the book, it says to create a 'hello_view.ex', and it's under the view section in MVC. But there is already a view in templates. This feels very confusing.
Also, they told me to put hello_world.html inside 'hello' folder in templates. Can I change this folder name? Why can't I rename it? In 'hello_controller.ex', it says 'hello_world.html', not 'hello/hello_world.html'

Answer 1

Phoenix views aren't HTML templates with embedded programming language like html.erb, but the names are similar to the ones in Django, where view means code for displaying data and template means actual HTML with embedded Elixir code (and they have extension eex).
According to the official guide for Phoenix Framework, short info about views:
They also act as a presentation layer for raw data from the controller, preparing it for use in a template. Functions which perform this transformation should go in a view.
Check this out:
Ruby on Rails flow:
router.rb -> Controller (-> Model) -> view in html.erb
Django flow:
urls.py -> View (act like Controller) -> Template
Phoenix flow:
endpoint (in lib) -> router (in web) -> Controller -> View -> Template
The Phoenix flow seems to be longer, but it's not. The biggest advantage for you:
You have explicit control over the middleware!
Remember that- framework does the magic for you, but explicitly. You exactly see what macros and other stuff are called.
Edit
Check out the stuff that's imported when using use in your code.
In your controller you're using Phoenix.Controller stuff, which provides you render function.
You call render with conn, template and assigns parameters. In deps/phoenix/lib/phoenix/controller.ex you have this render
function stored and in the private function do_render line:
view = Map.get(conn.private, :phoenix_view) ||
raise "a view module was not specified, set one with put_view/2"
Gets your View name from the current connection.
And few lines later uses it:
Phoenix.View.render_to_iodata(view, template, Map.put(conn.assigns, :conn, conn))
This call uses internally render in deps/phoenix/lib/phoenix/view.ex
and then render_within, but the name of the folder is set in __using__
use Phoenix.Template, Phoenix.View.__template_options__(__MODULE__, unquote(opts))
which calls __template__options where following lines are placed:
module
|> Module.split()
|> Enum.take(1)
|> Module.concat()
which does the Hello from Hello.PageView or whatever the name is.
Edit2
About changing default view in controller (info from Phoenix documentation):
By default, Controllers render templates in a view with a similar name
to the controller. For example, MyApp.UserController will render
templates inside the MyApp.UserView. This information can be
changed any time by using render/3, render/4 or the put_view/2
function:
def show(conn, _params) do
render(conn, MyApp.SpecialView, :show, message: "Hello")
end
def show(conn, _params) do
conn
|> put_view(MyApp.SpecialView)
|> render(:show, message: "Hello")
end