JPA Entity Mapping with Relationships

import jakarta.persistence.*;
import java.time.LocalDateTime;
import java.util.*;

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

    @Column(nullable = false, length = 100)
    private String name;

    @Column(unique = true, nullable = false)
    private String email;

    // One user has many orders
    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Order> orders = new ArrayList<>();

    // Many users belong to many roles
    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(
        name = "user_roles",
        joinColumns = @JoinColumn(name = "user_id"),
        inverseJoinColumns = @JoinColumn(name = "role_id")
    )
    private Set<Role> roles = new HashSet<>();

    @Column(updatable = false)
    private LocalDateTime createdAt;

    @PrePersist
    void onCreate() { createdAt = LocalDateTime.now(); }

    // Helper methods to manage bidirectional relationship
    public void addOrder(Order order) {
        orders.add(order);
        order.setUser(this);
    }

    public void removeOrder(Order order) {
        orders.remove(order);
        order.setUser(null);
    }

    // getters, setters omitted for brevity
}

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

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id", nullable = false)
    private User user;

    @Column(nullable = false)
    private Double amount;

    @Enumerated(EnumType.STRING)
    private OrderStatus status = OrderStatus.PENDING;
}

enum OrderStatus { PENDING, CONFIRMED, SHIPPED, DELIVERED, CANCELLED }

@Entity
public class Role {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(unique = true)
    private String name;
}