← Previous Next →

🛢️ Chapter 5: Database Integration with Spring Data JPA

Now that your Todo app has a clean architecture with a service and repository layer, it’s time to connect it to a real database using Spring Data JPA and PostgreSQL.

---

🚀 What You’ll Build

• A Todo entity mapped to a todos database table
• A Spring Data JPA TodoRepository
• Integration with PostgreSQL via Docker
• Ability to query and persist data from a real database

---

🧱 Step 1: Set Up PostgreSQL via Docker

Create a docker-compose.yml:

version: '3.8'
services:
  postgres:
    image: postgres:15
    container_name: todo-postgres
    environment:
      POSTGRES_USER: todo_user
      POSTGRES_PASSWORD: secret
      POSTGRES_DB: todo_db
    ports:
      - '5432:5432'

Run:

docker-compose up -d

---

⚙️ Step 2: Configure application.properties

spring.datasource.url=jdbc:postgresql://localhost:5432/todo_db
spring.datasource.username=todo_user
spring.datasource.password=secret
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect

---

🧠 Step 3: Define JPA Entity

Todo Entity (Simplified, No User Reference)

@Entity
@Table(name = "todos")
public class Todo {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private String title;

    private String description;

    @Column(nullable = false)
    private boolean completed;

    private Instant createdAt = Instant.now();

    // Getters and Setters
}

This version removes the User entity to keep the design focused and simple. You can add User later if authentication or multi-user support is needed.

---

📂 Repository Layer

@Repository
public interface TodoRepository extends JpaRepository<Todo, Long> {
    // You don't need to declare common methods like findAll, findById, save, deleteById
    // Spring Data JPA provides them out of the box.
}

❓ Why so few methods?

Although this interface appears empty, it inherits many powerful methods from JpaRepository<Todo, Long>, such as:

• findAll()
• findById(Long id)
• save(Todo todo)
• deleteById(Long id)

Spring Data JPA dynamically implements these using method name conventions and proxy objects.

---

🧪 Service Layer

@Service
public class TodoServiceImpl implements TodoService {
    private final TodoRepository todoRepository;

    @Autowired
    public TodoServiceImpl(TodoRepository todoRepository) {
        this.todoRepository = todoRepository;
    }

    public List<Todo> findAll() {
        return todoRepository.findAll();
    }

    public Todo findById(Long id) {
        return todoRepository.findById(id).orElseThrow();
    }

    public Todo create(Todo todo) {
        return todoRepository.save(todo);
    }

    public Todo update(Long id, Todo updatedTodo) {
        Todo existing = findById(id);
        updatedTodo.setId(existing.getId());
        return todoRepository.save(updatedTodo);
    }

    public void delete(Long id) {
        todoRepository.deleteById(id);
    }
}

---

🌐 Controller Layer

@RestController
@RequestMapping("/api/todos")
public class TodoController {
    private final TodoService todoService;

    public TodoController(TodoService todoService) {
        this.todoService = todoService;
    }

    @GetMapping
    public ResponseEntity<List<Todo>> getAllTodos() {
        return ResponseEntity.ok(todoService.findAll());
    }

    @GetMapping("/{id}")
    public ResponseEntity<Todo> getTodoById(@PathVariable Long id) {
        return ResponseEntity.ok(todoService.findById(id));
    }

    @PostMapping
    public ResponseEntity<Todo> createTodo(@RequestBody Todo todo) {
        return ResponseEntity.ok(todoService.create(todo));
    }

    @PutMapping("/{id}")
    public ResponseEntity<Todo> updateTodo(@PathVariable Long id, @RequestBody Todo todo) {
        return ResponseEntity.ok(todoService.update(id, todo));
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteTodo(@PathVariable Long id) {
        todoService.delete(id);
        return ResponseEntity.noContent().build();
    }
}

---

✅ Test with curl

# Create
curl -X POST -H "Content-Type: application/json" \
    -d '{"title":"Buy milk","description":"2% organic","completed":false}' \
    http://localhost:8080/api/todos

# Get all
curl http://localhost:8080/api/todos

# Update
curl -X PUT -H "Content-Type: application/json" \
    -d '{"title":"Buy almond milk","description":"Unsweetened","completed":true}' \
    http://localhost:8080/api/todos/1

# Delete
curl -X DELETE http://localhost:8080/api/todos/1

---

✅ Summary

• Connected your app to PostgreSQL using Spring Data JPA
• Used JpaRepository to simplify data access
• Defined a Todo JPA entity without user dependency
• Configured Docker for database setup
• Tested everything using curl

Next: Testing & Coverage ➡️

← Previous Next →