การสร้างเอนทิตีและคลังข้อมูล

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;

    public Product() {}

    public Product(String name, double price) {
        this.name = name;
        this.price = price;
    }

    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }

    @Override
    public String toString() {
        return "Product{" +
               "id=" + id +
               ", name='" + name + '\'' +
               ", price=" + price +
               '}';
    }
}

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {
    // Spring Data JPA automatically provides methods like:
    // save(), findById(), findAll(), deleteById(), etc.
}

// --- Simulated Product Entity --- //
class Product {
    private Long id;
    private String name;
    private double price;

    public Product(Long id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }
    // Getters and Setters (simplified for brevity)
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }

    @Override
    public String toString() {
        return "Product{id=" + id + ", name='" + name + "', price=" + price + "}";
    }
}

// --- Simulated Product Repository Interface --- //
interface ProductRepository {
    Product save(Product product);
}

// --- Simulated Product Repository Implementation --- //
class SimpleProductRepository implements ProductRepository {
    private static Long nextId = 1L;
    @Override
    public Product save(Product product) {
        if (product.getId() == null) {
            product.setId(nextId++); // Assign a new ID
        }
        System.out.println("Simulating save: " + product);
        return product;
    }
}

public class Main {
    public static void main(String[] args) {
        // 1. Create a Product entity instance
        Product newProduct = new Product(null, "Wireless Earbuds", 99.99);
        System.out.println("Created product: " + newProduct);

        // 2. Simulate saving it using our repository
        ProductRepository repository = new SimpleProductRepository();
        Product savedProduct = repository.save(newProduct);

        System.out.println("Product after simulated save: " + savedProduct);
    }
}