Elixir and Phoenix:

in elixir .ex is for compiled code .exs if for interpreted code

Hello World from Elixir (.exs one)

IO.puts("Hello World from elixirel")

Mix is build tool for elexir it allows us to

• create our project ( mix new project-name )
• compile our project(mix compile)
• run our project

Variable and constant:

defmodule Example do
  use Application
  @x 5 
  def start(_type,_args) do
    Example.main()
    Supervisor.start_link([],strategy: :one_for_one)
  end
  def main do
    name="Saugat"
    status=:gold
    IO.puts("name: #{name} status: #{status} constant no: #{@x}")
  end
end

If statement:

defmodule Example do
  use Application
  def start(_type,_args) do
    Example.main()
    Supervisor.start_link([],strategy: :one_for_one)
  end
  def main do
    name="Saugat"
    status=Enum.random([:gold,:silver,:bronze])
    if status===:gold do
      IO.puts("Welcome to Fancy lounge, #{name} ")
    else
      IO.puts("Get lost")
    end
  end
end

Case statement:

defmodule Example do

  use Application

  def start(_type,_args) do
    Example.main()

    Supervisor.start_link([],strategy: :one_for_one)
  end
  def main do
    name="Saugat"
    status=Enum.random([:gold,:silver,:bronze,:"not a member"])
    case status do
      :gold->IO.puts("Welcome to the fancy laung, #{name} ")
      :silver->IO.puts("Come in sir")
      :bronze->IO.puts("Come in")
      :"not a member"->IO.puts("Get subscribed");
      _->IO.puts("Get lost")
    end

  end

end

String interpolation and Hex in elixir: Hex is .........

defmodule Example do

  use Application

  

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  

  def main do

    IO.puts("This\nis\n\tmessage\n")

    IO.puts("After")

    IO.puts("String interpoluayion looks like \#{}")

    #numeric representation of unicode

    IO.puts(?a)

  end

end

Number and Number methods Integer and float in Elixir:

defmodule Example do
  use Application
  def start(_type, _args) do
    Example.main()
    Supervisor.start_link([], strategy: :one_for_one)
  end
  def main do
    a=10
    a=a+10.0
    b=3
    IO.puts(a/b)
    :io.format("~20f\n",[0.1])
    IO.puts(Float.ceil(1.6))
    IO.puts(Float.ceil(1.1,1))
    IO.puts(Integer.gcd(20,5))
  end

end

Compount types

• Date Time

defmodule Example do

  use Application

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  def main do

    # Create a specific time (16:30:00)

    time = Time.new!(16, 30, 0, 0)

    # Create a specific date (January 1, 2025)

    date = Date.new!(2025, 1, 1)

  

    # Combine the date and time into a DateTime in the UTC timezone

    date_time = DateTime.new!(date, time, "Etc/UTC")

  

    # Print the date, time, and combined DateTime

    IO.inspect(date, label: "Date")

    IO.inspect(time, label: "Time")

    IO.inspect(date_time, label: "DateTime")


    # Create a future DateTime (January 1, 2082, 00:00:00 UTC)

    future_time = DateTime.new!(Date.new!(2082, 1, 1), Time.new!(0, 0, 0, 0), "Etc/UTC")

    # Calculate the difference in seconds between now and the future time

    time_till = DateTime.diff(DateTime.utc_now(), future_time)

    # Print the total seconds until the future time

    IO.puts("Total seconds until future time: #{time_till}")

    # Calculate the number of days from the total seconds

    days = div(time_till, 86_400) # 86,400 seconds in a day

    # Print the remaining seconds after dividing by days

    IO.puts("Remaining seconds after days: #{rem(time_till, 86_400)}")

    # Calculate the number of hours from the remaining seconds

    hours = div(rem(time_till, 86_400), 60 * 60) # 60 * 60 seconds in an hour

    # Calculate the number of minutes from the remaining seconds after hours

    mins = div(rem(time_till, 60 * 60), 60) # 60 seconds in a minute

    IO.puts(

      "Time until 2082: #{days} days, #{hours} hours, #{mins} minutes"

    )

  end

end

Touple:

defmodule Example do

  use Application

  

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  

  def main do

    membership={:bronz,:silver}

    membership=Tuple.append(membership,":gold")

    IO.inspect(membership)

    prices={5,10,15}

    avg=Tuple.sum(prices)/tuple_size(prices)

    IO.puts(avg)

    IO.puts("Average price from #{elem(membership,0)} #{elem(membership,1)} #{elem(membership,2)} avg is #{avg}")

    user1={"Saugat",:gold}

    user2={"Hari",:silver}

    user3={"Sits",:bronz}

    {name,membership}=user1

    IO.puts("#{name} has a #{membership} membership")

    {name,membership}=user2

    IO.puts("#{name} has a #{membership} membership")

    {name,membership}=user3

    IO.puts("#{name} has a #{membership} membership")

  end

end

List and Loop:

defmodule Example do

  use Application

  

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  
  def main do

    users=[

      {"Saugat",:gold},

      {"Hari",:silver},

      {"Sits",:bronz},

      {"John",:bronz},

    ]
  Enum.each(users,fn {name,membership}->IO.puts("#{name} has a #{membership} membership")

  end

  )
  

  end

end

Mapping :

defmodule Example do

  use Application

  

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  

  def main do

    # :apple type str is called adem

    prices=%{

      gold: 25,

      silver: 20,

      bronze: 25,

      none: 0,

  

    }

    memberships=%{

      gold: :gold ,

      silver: :silver,

      bronze: :bronze,

      none: :none

    }

  

    users=[

      {"Saugat",memberships.gold},

      {"Hari",memberships.silver},

      {"Sits",memberships.bronze},

      {"John",memberships.bronze},

    ]

  Enum.each(users,fn {name,membership}->IO.puts("#{name} has a #{membership} membership which price is #{prices[membership]}")

  end

  )

  

  end

end

Structs :

defmodule Membership do

  defstruct [:type, :price]

end

  

defmodule User do

  defstruct [:name, :membership]

end

  

defmodule Example do

  use Application

  

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  

  def main do

    # :apple type str is called adem

  

    gold_membership = %Membership{type: :gold, price: 25}

    silver_membership = %Membership{type: :silver, price: 20}

    bronze_membership = %Membership{type: :bronze, price: 15}

    none_membership = %Membership{type: :none, price: 0}

  

    users = [

      %User{name: "Saugat", membership: gold_membership},

      %User{name: "Hari", membership: silver_membership},

      %User{name: "Sits", membership: bronze_membership},

      %User{name: "John", membership: none_membership}

    ]

  

    Enum.each(users, fn %User{name: name,membership: membership} ->

      IO.puts("#{name} has a #{membership.type} membership which price is #{membership.price}")

    end)

  end

end

Number guessing game:

defmodule Example do

  use Application

  

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  

  def main do

    correct=:rand.uniform(11)-1

    guess=IO.gets("Guess a number between 0 & 10: ") |> String.trim() ##method chaining

    if String.to_integer(guess)==correct do

      IO.puts("You won")

    else

      IO.puts("You lost")

    end

    IO.puts("You guess #{guess} , correct was #{correct}")

  end

end

Cases and pattern Matching

defmodule Example do

  use Application

  

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  

  def main do

    correct=:rand.uniform(11)-1

    guess=IO.gets("Guess a number between 0 & 10: ") |> String.trim() |> Integer.parse() ##method chaining

    IO.inspect(guess)

   case guess do

     {result, ""}->IO.puts("parse sucessful #{result}")

     {result,other}->IO.puts("parse partially sucessful #{result} and #{other}")

    :error->IO.puts("Something went wrong !")

   end

  end

end

Game of above using case and pattern matching:

defmodule Example do

  use Application

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  def main do

    correct=:rand.uniform(11)-1

    guess=IO.gets("Guess a number between 0 & 10: ") |> String.trim() |> Integer.parse() ##method chaining

    IO.inspect(guess)

   case guess do

     {result, _}->

      IO.puts("parse sucessful #{result}")

      if result===correct do

        IO.puts("You won")

      else

        IO.puts("You lose the correct ans is : #{correct}")

      end

    :error->IO.puts("The correct !")

   end

  end

end

Lists and List comprehension:

defmodule Example do

  require Integer

  use Application

  

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  

  def main do

    grades=[25,50,75,100]

    for n <- grades do

       IO.puts(n)

    end

  

    grades=[25,50,75,100]

    new= for n <- grades,do: n+5

    new=new ++ [125]

    new=new ++ [150,175]

    IO.inspect(new)

    final=[5|new]

    IO.inspect(final)

    even=for n <- final,rem(n,2)==0, do: n

    # even=for n <- final,Integer.is_even(n)==0, do: n

    IO.inspect(even)

  

  end

  

end

functional programming and Defining Custom function

defmodule Example do

  require Integer

  use Application

  

  def start(_type, _args) do

    Example.main()

    Supervisor.start_link([], strategy: :one_for_one)

  end

  # function that takes numbers then return sum and average

  def sum_and_average(numbers) do

    sum=Enum.sum(numbers)

    average=sum/Enum.count(numbers)

    {sum,average}

  end

  @spec print_numbers(any()) :: none()

  def print_numbers(numbers) do

    numbers |> Enum.join(" ") |> IO.puts()

  end

  def get_numbers_from_user do

    IO.puts("Enter number seperated by spaces:> ")

    user_input=IO.gets("") |>String.trim()

    String.split(user_input," ")|>Enum.map(&String.to_integer/1)

  end

  def main do

  user_given_numbers=get_numbers_from_user()

 IO.inspect(sum_and_average(user_given_numbers))

 {sum,average}=sum_and_average(user_given_numbers)

 IO.puts("The sum is #{sum} and the average is #{average}")

   numbers =[1,2,3,4,5,6]

   #ananomus function

   Enum.each(numbers,fn num->IO.puts(num) end)

   numbers =["1","2","3","4","5","6"]

  #  passing function as argument with &

   result=Enum.map(numbers,&String.to_integer/1)

    IO.inspect(sum_and_average(result))

  

  end

  

end

Phoenix Start:

✅ Phoenix App Setup Summary

Phoenix is a web framework built on Elixir, designed for high performance, scalability, and maintainability. It is particularly well-suited for real-time applications and APIs. If you're coming from frameworks like Django, Express, or Rails, this guide will help you get started with Phoenix.

---

1. Install Hex (Elixir package manager)

Hex is the package manager for the Elixir ecosystem, similar to npm for Node.js or pip for Python. It is used to manage dependencies in your Phoenix project.

mix local.hex

• What it does: Installs or updates Hex locally.
• Where it stores Hex: ~/.mix/archives/

---

2. Install Phoenix Project Generator

The Phoenix project generator (phx_new) scaffolds a new Phoenix project with all the necessary files and dependencies.

mix archive.install hex phx_new

• What it does: Installs the phx_new archive, which is used to generate new Phoenix projects.
• Versioning: The latest version (e.g., 1.7.21) is stored as an .ez archive.

---

3. Generate a New Phoenix App

This command creates a new Phoenix project with a specified name and database backend.

mix phx.new forum --database sqlite3

• What it does:

  • Creates a new app named forum.
  • Sets up the project structure.
  • Installs dependencies.
  • Configures SQLite3 as the database backend (you can also use PostgreSQL or MySQL).

• Key Flags:

  • --database sqlite3: Specifies the database adapter. Replace sqlite3 with postgres or mysql if needed.

---

4. Navigate into the App Folder

cd forum

• Why?: Phoenix commands like mix phx.server and mix ecto.create must be run from within the project folder to access the mix.exs file and configuration files.

---

5. Create the Database

mix ecto.create

• What it does:

  • Compiles the project (if not already compiled).
  • Creates the database using Ecto, Phoenix's database wrapper and query generator.

• Ecto: Think of Ecto as the ORM (like Django ORM or Sequelize). It handles database migrations, queries, and schema definitions.

---

6. Run the Phoenix Server

mix phx.server

• What it does:

  • Starts the Phoenix web server (default: http://localhost:4000).
  • Watches for code changes and recompiles automatically.

• Default Web Server: Phoenix uses the Cowboy web server, which is highly performant and lightweight.

---

7. (Optional) Run Phoenix with IEx

iex -S mix phx.server

• What it does:
  • Starts the Phoenix server with the interactive Elixir shell (IEx).
  • Useful for debugging, testing database queries, and exploring the application state.

---

⚠️ Note: Symlink Warning on Windows

If you see a warning like:

“Phoenix is unable to create symlinks...”

Fix:

1. Run your terminal as Administrator at least once.
2. Phoenix will then be able to create symlinks for faster reloads.

---

📁 Phoenix Directory Structure vs Django vs Express

Phoenix organizes its files in a way that promotes separation of concerns. Here's how it compares to Django and Express:

✅ Root-Level Overview

Path	Phoenix Purpose	Django Equivalent	Express Equivalent
mix.exs	Project config (like package.json)	settings.py, pyproject.toml	package.json
config/	App and database configs	settings.py, env.py	.env, config files
lib/	Main application code	Django project/ folder	src/ or main app folder
test/	Unit tests (ExUnit)	tests/	test/, __tests__/
.formatter.exs	Elixir code formatting	pyproject.toml (Black)	.prettierrc, .eslintrc
assets/	JavaScript/CSS (frontend assets)	static/, templates/	public/, views/

---

🔹 Inside lib/ (Main App Code)

Path	Phoenix Purpose	Django Equivalent	Express Equivalent
forum.ex	Main app entrypoint	__init__.py	index.js, app.js
forum/application.ex	Supervision tree / app lifecycle	Not applicable	App setup in app.js
forum_web/	Web layer: routes, controllers, templates	Views, URLs, templates	Routes & views

---

🔹 Inside lib/forum_web/ (Phoenix Web Layer)

Path	Phoenix Purpose	Django Equivalent	Express Equivalent
controllers/	Request logic handlers	views.py	Route handler functions
views/	Rendering logic (separate from controllers)	Context processors	Templating logic (optional)
templates/	EEx templates (HTML)	templates/	EJS/Pug templates
router.ex	Route definitions	urls.py	app.get(), app.post()
endpoint.ex	Entry point for HTTP requests (Bandit/Cowboy)	WSGI application	Express app (app)

---

🔹 Database, Migrations & ORM

Path	Phoenix Purpose	Django Equivalent	Express Equivalent
priv/repo/migrations/	Ecto migration files	migrations/	Sequelize/Mongoose files
lib/forum/repo.ex	Ecto Repo for DB operations	Django ORM	Mongoose/Sequelize
schema files (*.ex)	Define database schema + changesets	models.py	Models in Mongoose/ORM

---

🔹 Frontend

Path	Phoenix Purpose	Django Equivalent	Express Equivalent
assets/js/	JavaScript (esbuild or webpack)	Static JS in static/	public/ or views/
assets/css/	CSS stylesheets	Static CSS in static/	Same
assets/	Overall frontend pipeline	Django static/ + templates/	public/ or static files

---

🔹 Common Tasks

Task	Phoenix	Django	Express
Generate project	mix phx.new app_name	django-admin startproject	express-generator (optional)
Run dev server	mix phx.server	python manage.py runserver	node app.js or nodemon
Migrate DB	mix ecto.migrate	python manage.py migrate	ORM-dependent
Create migration	mix ecto.gen.migration	python manage.py makemigrations	ORM-dependent
Create model/schema	mix phx.gen.schema	Django models	ORM-dependent

---

🧠 TL;DR: Concept Mapping

Concept	Phoenix	Django	Express
Project Config	mix.exs	settings.py	package.json
Routing	router.ex	urls.py	app.get() etc.
Controllers	controllers/	views.py	Route handlers
Templates	templates/	templates/	EJS/Pug views
ORM/Models	schema + changeset	Django Models	Mongoose/Sequelize
DB Migrations	ecto.migrations	Django migrations	ORM-based tools
Frontend	assets/	static/	public/

---

📦 Phoenix JSON API Generator: mix phx.gen.json

Phoenix provides a powerful generator for creating JSON APIs. This is particularly useful for API-first applications or when building a backend for a frontend framework like React or Vue.

---

✅ Command

mix phx.gen.json Posts Post posts body:string title:string

---

🧠 Breakdown

Part	Description
mix phx.gen.json	Generates a JSON-only resource (no HTML views/templates).
Posts (Context)	A module grouping logic (e.g., Forum.Posts).
Post (Schema)	The database model (e.g., Posts.Post).
posts (DB Table)	Table name used in the DB (plural of schema).
body:string	Adds :body field (type :string).
title:string	Adds :title field (type :string).

---

📁 Files Generated

🔹 Context & Schema

File	Purpose
lib/forum/posts/post.ex	Defines the Post Ecto schema.
lib/forum/posts.ex	CRUD functions (context): list_posts/0, create_post/1, etc.

🔹 Migration

File	Purpose
priv/repo/migrations/*_create_posts.exs	Migration to create the posts table.

🔹 Controller & View

File	Purpose
lib/forum_web/controllers/post_controller.ex	Handles API endpoints.
lib/forum_web/views/post_json.ex	Formats JSON responses.

🔹 Router Update

Adds:

scope "/api", ForumWeb do
  pipe_through :api
  resources "/posts", PostController, except: [:new, :edit]
end

---

🛠️ After the Generator

1. Run the Migration

mix ecto.migrate

2. Start the Server

mix phx.server

3. API Endpoints (Default)

Method	Route	Action
GET	/api/posts	List posts
GET	/api/posts/:id	Show post
POST	/api/posts	Create post
PUT	/api/posts/:id	Update post
DELETE	/api/posts/:id	Delete post

---

✅ Summary

Phoenix is a powerful framework for building scalable, maintainable web applications. It provides a clean separation of concerns with contexts, schemas, and controllers. The mix tool simplifies common tasks like generating code, running migrations, and starting the server. Phoenix is ideal for API-first applications or real-time features using WebSockets.

---

mix phx.gen.json Accounts User users name:string email:string:unique

🧠 Breakdown

Part	Description
mix phx.gen.json	Generates a JSON-only resource (no HTML views/templates).
Accounts (Context)	The context module that groups related logic (e.g., Forum.Accounts).
User (Schema)	The schema module for User (e.g., Accounts.User).
users (DB Table)	The name of the table in the database (e.g., users).
name:string	Adds a name field (type string).
email:string:unique	Adds an email field (type string) with a unique constraint to ensure no duplicate emails.

---

📁 Files Generated

🔹 Context and Schema (in lib/forum/)

File	Purpose
lib/forum/accounts/user.ex	Defines the User schema with name and email fields.
lib/forum/accounts.ex	Context module for Accounts, containing functions for CRUD operations on users.

🔹 Migration (in priv/repo/migrations/)

File	Purpose
*_create_users.exs	Migration to create the users table with name and email fields, and ensure the email field is unique.

🔹 Controller and View (in lib/forum_web/)

File	Purpose
lib/forum_web/controllers/user_controller.ex	Handles API requests for users.
lib/forum_web/views/user_json.ex	Renders JSON responses for users.

🔹 Router Update (in router.ex)

Adds the following route to handle user-related API requests:

scope "/api", ForumWeb do
  pipe_through :api
  resources "/users", UserController, except: [:new, :edit]
end

---

🛠️ Next Steps

1. Run the Migration

Ensure your database is updated to reflect the changes:

mix ecto.migrate

2. Start the Phoenix Server

Run your server to start receiving requests:

mix phx.server

3. API Endpoints (for /api/users)

Method	Route	Action
GET	/api/users	List users
GET	/api/users/:id	Show user
POST	/api/users	Create user
PUT	/api/users/:id	Update user
DELETE	/api/users/:id	Delete user

---

🔁 Concept Mapping

Phoenix JSON Generator	Django Equivalent	Express Equivalent
mix phx.gen.json	Django REST Framework (DRF) ViewSet	Express + Mongoose/Sequelize
Context	Django accounts/ app	Folder/module for accounts
Schema	Django models.py for User	Mongoose schema for User
Controller	DRF ViewSet for User	Express route/controller
Migration	Django makemigrations + migrate	Sequelize migration

---

✅ Summary

• The mix phx.gen.json command simplifies the creation of JSON APIs in Phoenix.
• It generates a clean separation of concerns with context, schema, controller, and view files.
• The generated API is ready to handle CRUD operations for the User resource.
• Phoenix's mix tool ensures a streamlined development process, from migrations to server setup.

---