Hibernate Entity Mapping Explained

package io.thecodeforge.entities;

import jakarta.persistence.*;
import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;
import java.time.LocalDateTime;

/**
 * io.thecodeforge: Production-grade Entity Mapping
 * Utilizing Hibernate-specific enhancements for audit logging.
 */
@Entity
@Table(name = "forge_users", indexes = {
    @Index(name = "idx_username", columnList = "username"),
    @Index(name = "idx_email", columnList = "email_address")
})
public class UserAccount {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "username", nullable = false, unique = true, length = 50)
    private String username;

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

    @Enumerated(EnumType.STRING)
    @Column(name = "account_status", nullable = false)
    private AccountStatus status = AccountStatus.ACTIVE;

    @CreationTimestamp
    @Column(name = "created_at", updatable = false)
    private LocalDateTime createdAt;

    @UpdateTimestamp
    @Column(name = "updated_at")
    private LocalDateTime updatedAt;

    public enum AccountStatus {
        ACTIVE, SUSPENDED, DELETED
    }

    // Standard Getters/Setters
}

package io.thecodeforge.entities;

import jakarta.persistence.*;
import java.util.ArrayList;
import java.util.List;

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

    private String name;

    // CORRECT: mappedBy refers to the field name in the Employee class
    // This side is the 'Inverse' side; it does not control the foreign key.
    @OneToMany(mappedBy = "department", cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
    private List<Employee> employees = new ArrayList<>();

    // Helper method to keep both sides of the relationship in sync
    public void addEmployee(Employee employee) {
        employees.add(employee);
        employee.setDepartment(this);
    }
}

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

    private String fullName;

    // This is the 'Owning' side. It contains the @JoinColumn (Foreign Key).
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "dept_id", nullable = false)
    private Department department;

    public void setDepartment(Department department) {
        this.department = department;
    }
}