Hibernate Mapping

package com.example.entity;

import jakarta.persistence.*;
import java.util.Date;

@Entity
@Table(name = "employees",
       uniqueConstraints = @UniqueConstraint(columnNames = {"email"}),
       indexes = @Index(name = "idx_dept", columnList = "department_id"))
public class Employee {

    // AUTO: Hibernate picks best strategy
    // IDENTITY: DB auto-increment (MySQL)
    // SEQUENCE: DB sequence (PostgreSQL, Oracle)
    // TABLE: Hibernate-managed table (portable)
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "first_name", nullable = false, length = 50)
    private String firstName;

    @Column(name = "last_name", nullable = false, length = 50)
    private String lastName;

    @Column(nullable = false, unique = true, length = 100)
    private String email;

    @Column(precision = 10, scale = 2) // DECIMAL(10,2)
    private java.math.BigDecimal salary;

    // @Temporal for java.util.Date (not needed for java.time.*)
    @Temporal(TemporalType.DATE)
    @Column(name = "hire_date")
    private Date hireDate;

    // Store enum as string "FULL_TIME", "PART_TIME", "CONTRACT"
    @Enumerated(EnumType.STRING)
    @Column(name = "employment_type", nullable = false)
    private EmploymentType employmentType = EmploymentType.FULL_TIME;

    // Large text field (CLOB/TEXT)
    @Lob
    @Column(name = "bio")
    private String bio;

    // Large binary field (BLOB)
    @Lob
    @Column(name = "profile_photo")
    private byte[] profilePhoto;

    // Not persisted to DB
    @Transient
    private String fullName;

    // Computed field
    public String getFullName() {
        return firstName + " " + lastName;
    }

    public enum EmploymentType { FULL_TIME, PART_TIME, CONTRACT }

    // Constructors, getters, setters...
}

// IDENTITY - uses DB auto-increment (MySQL, SQL Server)
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

// SEQUENCE - uses DB sequence (PostgreSQL, Oracle)
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "user_seq")
@SequenceGenerator(name = "user_seq", sequenceName = "user_sequence",
                   allocationSize = 50) // Fetch 50 IDs at once for performance
private Long id;

// TABLE - uses a separate table to track IDs (portable, but slow)
@Id
@GeneratedValue(strategy = GenerationType.TABLE, generator = "user_table_gen")
@TableGenerator(name = "user_table_gen", table = "id_generator",
                pkColumnName = "gen_name", valueColumnName = "gen_value",
                pkColumnValue = "user_id", allocationSize = 1)
private Long id;

// UUID - generates UUID string
@Id
@GeneratedValue(strategy = GenerationType.UUID)
private String id; // e.g., "550e8400-e29b-41d4-a716-446655440000"

// Manual ID (no generation)
@Id
private String productCode; // You set this manually

// @Embeddable: value object embedded in another entity
@Embeddable
public class Address {
    private String street;
    private String city;
    private String state;
    private String zipCode;
    private String country;
    // getters/setters
}

// @Embedded: embed the Address in User
@Entity
public class User {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @Embedded
    @AttributeOverrides({
        @AttributeOverride(name = "street", column = @Column(name = "home_street")),
        @AttributeOverride(name = "city",   column = @Column(name = "home_city"))
    })
    private Address homeAddress;

    @Embedded
    @AttributeOverrides({
        @AttributeOverride(name = "street", column = @Column(name = "work_street")),
        @AttributeOverride(name = "city",   column = @Column(name = "work_city"))
    })
    private Address workAddress;
}