Lecture: Designing Instagram's Backend in Django

Lecture Flow

1. Discuss design
2. Database schemas
3. Dive into coding

System Design

• Server: One Django server running with default SQLite DB
• Clients: Multiple clients interacting with the server

Core Features

• Models: Post and User (primary models)
  • Post: Includes images, text, and descriptions
  • User: Authenticated users
  • PostComment: Comments on posts
  • UserFollow: Tracks followers and followees
  • PostLike: Tracks who liked which posts

Initial Setup

• Create a Python environment: source insta/bin/activate
• Install Django and Django Rest Framework: pip install Django djangorestframework
• Create Django project: django-admin startproject Instagram
• Create a new app: python manage.py startapp app
• Modify settings.py to include app and rest_framework
• Modify urls.py to include app's URLs

Database Schema

User Table

• userID (Primary Key)
• email
• username
• password
• first_name
• last_name
• bio (optional)
• created_at
• updated_at

Post Table

• postID (Primary Key)
• title
• description
• created_at
• updated_at
• user (Foreign Key)

PostComment Table

• commentID (Primary Key)
• comment_text
• created_at
• updated_at
• userID (Foreign Key)
• postID (Foreign Key)

PostLike Table

• likeID (Primary Key)
• userID (Foreign Key)
• postID (Foreign Key)

UserFollow Table

• followID (Primary Key)
• userID (Foreign Key)
• followeeID (Foreign Key)

Django Model Configurations

User Model

• Extend Django's default user model using AbstractUser
• Configure custom fields and default values (is_staff, is_active, is_superuser)
• Add custom manager class (UserManager) with methods to create users and superusers
• Settings update: Specify custom user model in settings.py

Post Model

• Define basic fields: title, description, created_at, updated_at, user

PostLike Model

• Define fields: userID, postID
• Ensure a user cannot like the same post more than once using unique_together

PostComment Model

• Define fields: comment_text, created_at, updated_at, userID, postID

UserFollow Model

• Define fields: userID, followeeID
• Ensure unique combinations of user and followee using unique_together

Serializers

• Create serializers for each model to handle validation and transformation of data

Views and APIs

User APIs

• Registration: Register a new user
• Login: Authenticate user and return a token
• Get User: Retrieve user by ID
• Update User: Edit user details
• Delete User: Remove a user from the database
• Follow User: Follow another user
• Unfollow User: Unfollow a user
• List User Posts: Retrieve all posts made by a user

Post APIs

• Create Post: Add a new post
• Retrieve Post: Get details of a post by ID
• Update Post: Modify an existing post
• Delete Post: Remove a post
• Like Post: Like or unlike a post
• Get Post Likes: Get all users who liked a post
• Add Comment: Comment on a post
• Get Comments: Retrieve all comments on a post

Testing

• Various test cases for each API using Django's development server and Django shell
• Validations for user creation, password checking, user token generation for login, and CRUD operations for posts and comments

Potential Enhancements

• Media handling by uploading media to S3 and storing URLs in the database
• Optimize using caching for follower/following counts on large scale