Spring Boot API – JPA, PostgreSQL & Docker

This project is a learning-focused Spring Boot REST API that demonstrates the full backend development lifecycle:

• Designing REST resources
• Applying JPA & Hibernate ORM
• Modeling entity relationships
• Migrating from an in-memory database (H2) to PostgreSQL
• Running PostgreSQL in Docker with persistent volumes

The project evolves step-by-step across multiple branches to clearly show progress and decisions.

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🧠 Project Goals

• Practice clean REST API design
• Understand JPA entity mapping and relationships
• Learn database migration (H2 → PostgreSQL)
• Learn Docker fundamentals for backend development
• Build something that can be reviewed, extended, and reused

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🗂️ Project Structure

├── topic
│   ├── Topic.java
│   ├── TopicRepository.java
│   ├── TopicService.java
│   └── TopicController.java
│
├── course
│   ├── Course.java
│   ├── CourseRepository.java
│   ├── CourseService.java
│   └── CourseController.java
│
├── lesson
│   ├── Lesson.java
│   ├── LessonRepository.java
│   ├── LessonService.java
│   └── LessonController.java
│
└── SpringbootApiApplication.java

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🔗 Domain Model & Relationships

The API models a simple learning platform: Topic → Course → Lesson

Relationships

• Topic → Course : One-to-Many
  • A topic can have many courses
  • A course must belong to exactly one topic
• Course → Lesson : One-to-Many
  • A course can have many lessons
  • A lesson must belong to exactly one course

JPA Mapping Strategy

• Relationships are unidirectional
• Foreign keys are stored on:
  • course.topic_id
  • lesson.course_id

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🌱 Branch Strategy

This repository intentionally uses multiple branches to show incremental development.

main

• Basic Spring Boot REST API
• CRUD for:
  • Topic
  • hello
• updated it to use ResponseEntity

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feature/jpa-persistence

• Introduced JPA & Hibernate
  • CRUD for:
  • Course
  • Lesson
• Added entity relationships:
  • Topic → Course
  • Course → Lesson
• Repository query methods:
  • findByTopicId
  • findByCourseId
• H2 in-memory database
• Verified behavior with Postman

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feature/postgres-docker

• Replaced H2 with PostgreSQL
• PostgreSQL runs in Docker
• Persistent storage via Docker volumes
• Spring Boot connects to PostgreSQL via JDBC
• Data persists across container restarts

This branch represents the current most complete version.

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🐳 Docker Setup (PostgreSQL)

The project uses Docker only for the database while the Springboot application stills runs locally.

Docker Compose

• Pulls official PostgreSQL image
• Exposes port 5432
• Uses a named volume for persistence

services:
  postgres:
    image: postgres:16
    container_name: springboot-postgres
    ports:
      - "5432:5432"
    environment:
      POSTGRES_DB: springbootdb
      POSTGRES_USER: springuser
      POSTGRES_PASSWORD: springpass
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:

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Application Configuration

inside application.properties (PostgreSQL):

spring.datasource.url=jdbc:postgresql://localhost:5432/springbootdb
spring.datasource.username=springuser
spring.datasource.password=springpass
spring.datasource.driver-class-name=org.postgresql.Driver

spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=update
spring.jpa.properties.hibernate.format_sql=true

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##How to Run the Project (PostgreSQL Version)

1.Start Docker Engine
2.Navigate to project root
3.Run:
    docker compose up
4.Run Spring Boot app from IntelliJ
5.API available at:
  **http://localhost:8080**

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##API Endpoints (Examples):

  --> GET /topics
  --> POST /topics

Courses:
  --> POST /topics/{topicId}/courses
  --> GET /topics/{topicId}/courses

Lessons:
  --> POST /courses/{courseId}/lessons
  --> GET /courses/{courseId}/lessons

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