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elearning/docs/api-docs/ER/README.md

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Database Schema (ERD) Documentation

📊 Entity-Relationship Diagram

Online Visualization

View the interactive ERD diagram:

📋 Database Overview

Total Tables: 17

Category Tables Count
Core users, categories, courses, chapters, lessons 5
Content quizzes, questions, choices, lesson_attachments 4
Progress enrollments, lesson_progress, quiz_attempts 3
Communication announcements, announcement_attachments 2
Commerce (อนาคต) orders, payments, withdrawals 3

🎯 Key Features

1. Multi-language Support

  • Uses jsonb fields for Thai/English content
  • Fields: title, content, description

2. Video Progress Tracking

  • Track playback position per student
  • Auto-complete at 90% watched
  • Resume from last position

3. Lesson Prerequisites

  • Sequential learning control
  • Quiz pass requirements
  • Flexible ordering

4. File Attachments

  • Multiple files per lesson
  • Support for PDF, DOCX, ZIP, images
  • Sortable with descriptions

5. Quiz System

  • Multiple attempts with cooldown
  • Score policies (HIGHEST/LATEST/FIRST/AVERAGE)
  • Detailed attempt history

📊 Main Entities

Users

  • Roles: STUDENT, INSTRUCTOR, ADMIN
  • Profile information
  • Authentication data

Courses

  • Multi-language titles and descriptions
  • Categories and pricing
  • Instructor ownership
  • Approval workflow

Chapters & Lessons

  • Hierarchical structure
  • Sort ordering
  • Multiple lesson types (video, pdf, text, quiz)
  • Prerequisites support

Progress Tracking

  • Enrollment status
  • Lesson completion
  • Video playback position
  • Quiz attempts and scores

🔗 Relationships

users (1) ──── (many) courses [instructor]
users (1) ──── (many) enrollments
users (1) ──── (many) lesson_progress
users (1) ──── (many) quiz_attempts

courses (1) ──── (many) chapters
courses (1) ──── (many) enrollments
courses (1) ──── (many) announcements

chapters (1) ──── (many) lessons

lessons (1) ──── (many) lesson_attachments
lessons (1) ──── (many) lesson_progress
lessons (1) ──── (many) quizzes

quizzes (1) ──── (many) questions
quizzes (1) ──── (many) quiz_attempts

questions (1) ──── (many) choices

🎨 How to Visualize

Using dbdiagram.io

  1. Open dbdiagram.io

  2. Import Schema

    • Click "Import" button (top right)
    • Select "From DBML"
    • Copy contents from ERD_v2_improved.txt
    • Paste into the editor
    • Click "Import"

  3. View Diagram

    • Zoom in/out with mouse wheel
    • Drag to pan
    • Click tables to highlight relationships
    • Export as PNG/PDF/SQL

Alternative Tools

  • DBeaver: Import SQL and generate ER diagram
  • MySQL Workbench: Reverse engineer from database
  • pgAdmin: PostgreSQL schema visualization
  • draw.io: Manual diagram creation

📝 Table Descriptions

Core Tables

users

  • User accounts and authentication
  • Roles: STUDENT, INSTRUCTOR, ADMIN
  • Profile information

categories

  • Course categorization
  • Multi-language names

courses

  • Course information and metadata
  • Pricing and approval status
  • Instructor ownership

chapters

  • Course structure organization
  • Sortable within courses

lessons

  • Learning content units
  • Types: video, pdf, text, quiz
  • Prerequisites and sequencing

Content Tables

quizzes

  • Assessment configuration
  • Attempt limits and cooldown
  • Passing score requirements

questions

  • Quiz questions
  • Types: multiple_choice, true_false
  • Point values

choices

  • Answer options for questions
  • Correct answer marking

lesson_attachments

  • Supplementary files
  • PDFs, documents, code samples
  • Multi-language descriptions

Progress Tables

enrollments

  • Student course registrations
  • Progress tracking
  • Certificate issuance

lesson_progress

  • Lesson completion status
  • Video playback position
  • Watch history

quiz_attempts

  • Quiz submission records
  • Scores and answers
  • Attempt history

Communication Tables

announcements

  • Course announcements
  • Pinning and scheduling
  • Multi-language content

announcement_attachments

  • Announcement file attachments

🔧 Database Constraints

Primary Keys

  • All tables use auto-incrementing integer PKs

Foreign Keys

  • Maintain referential integrity
  • Cascade deletes where appropriate

Unique Constraints

  • (user_id, course_id) in enrollments
  • (user_id, lesson_id) in lesson_progress
  • Email in users

Check Constraints (via notes)

  • Progress percentages: 0-100
  • Scores: 0-100
  • Sort orders: >= 0
  • Prices: >= 0

Indexes

  • Single column indexes on FKs
  • Composite indexes for common queries
  • JSONB GIN indexes for multi-language fields

🚀 Migration Notes

PostgreSQL Extensions Required

CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
CREATE EXTENSION IF NOT EXISTS "pg_trgm";  -- for text search

JSONB Usage

-- Multi-language fields
title JSONB  -- {"th": "...", "en": "..."}

-- Query examples
WHERE title->>'th' LIKE '%Python%'
WHERE title @> '{"en": "Introduction"}'

Soft Delete Pattern

-- Recommended for important tables
ALTER TABLE courses ADD COLUMN deleted_at TIMESTAMP;
CREATE INDEX idx_courses_deleted ON courses(deleted_at) WHERE deleted_at IS NULL;

📈 Performance Considerations

Indexes Created

  • All foreign keys
  • Composite indexes for (course_id, sort_order)
  • User email for login
  • Course status for filtering
  • Last watched timestamp for recent videos

Query Optimization

  • Use SELECT specific columns
  • Implement pagination
  • Cache course lists in Redis
  • Use database views for complex queries

🔗 Related Documentation

📊 Statistics

  • Total Tables: 17
  • Total Relationships: 20+
  • Multi-language Fields: 15+
  • Indexed Columns: 40+
  • JSONB Fields: 15+

🎯 Next Steps

  1. ✅ Review ERD schema
  2. ⏳ Create PostgreSQL database
  3. ⏳ Run migrations
  4. ⏳ Seed initial data
  5. ⏳ Implement API endpoints
  6. ⏳ Test with sample data

Last Updated: 2024-12-24
Version: 2.0 (Improved)