JPA - Entity Introduction

package model;
import jakarta.persistence.*;

/**
 * Represents a user entity in the application.
 */
@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id; // Unique identifier for the user.

    private String name; // The name of the user.

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "address_id", referencedColumnName = "id")
    private Address address; // The address associated with the user.

    /**
     * Retrieves the unique identifier of the user.
     * @return The user's ID.
     */
    public Long getId() {
        return id;
    }

    /**
     * Sets the unique identifier of the user.
     * @param id The user's ID.
     */
    public void setId(Long id) {
        this.id = id;
    }

    /**
     * Retrieves the name of the user.
     * @return The name of the user.
     */
    public String getName() {
        return name;
    }

    /**
     * Sets the name of the user.
     * @param name The name of the user.
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * Retrieves the address associated with the user.
     * @return The user's address.
     */
    public Address getAddress() {
        return address;
    }

    /**
     * Sets the address associated with the user.
     * @param address The user's address.
     */
    public void setAddress(Address address) {
        this.address = address;
    }
}

package model;

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

/**
 * Represents an address entity in the application.
 */
@Entity
public class Address {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id; // Unique identifier for the address.

    private String street; // The street of the address.

    private String city; // The city of the address.

    @OneToMany(mappedBy = "address", cascade = CascadeType.ALL)
    private List<User> users; // The list of users associated with this address.

    /**
     * Retrieves the unique identifier of the address.
     * @return The address ID.
     */
    public Long getId() {
        return id;
    }

    /**
     * Sets the unique identifier of the address.
     * @param id The address ID to set.
     */
    public void setId(Long id) {
        this.id = id;
    }

    /**
     * Retrieves the street of the address.
     * @return The street of the address.
     */
    public String getStreet() {
        return street;
    }

    /**
     * Sets the street of the address.
     * @param street The street to set for the address.
     */
    public void setStreet(String street) {
        this.street = street;
    }

    /**
     * Retrieves the city of the address.
     * @return The city of the address.
     */
    public String getCity() {
        return city;
    }

    /**
     * Sets the city of the address.
     * @param city The city to set for the address.
     */
    public void setCity(String city) {
        this.city = city;
    }

    /**
     * Retrieves the list of users associated with this address.
     * @return The list of users.
     */
    public List<User> getUsers() {
        return users;
    }

    /**
     * Sets the list of users associated with this address.
     * @param users The list of users to set.
     */
    public void setUsers(List<User> users) {
        this.users = users;
    }
}

import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.Persistence;
import model.Address;
import model.User;

/**
 * A class demonstrating basic usage of JPA (Java Persistence API).
 */
public class Main {
    public static void main(String[] args) {
        // Create EntityManagerFactory using persistence unit name
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("jpa-example");

        // Create EntityManager
        EntityManager em = emf.createEntityManager();

        // Create and persist a new user with address
        em.getTransaction().begin(); // Begin transaction
        Address address = new Address();
        address.setStreet("111 Srikakulam");
        address.setCity("City");
        em.persist(address); // Persist the address entity

        User user = new User();
        user.setName("Mahesh");
        user.setAddress(address);
        em.persist(user); // Persist the user entity along with associated address
        em.getTransaction().commit(); // Commit transaction

        // Retrieve user with associated address
        User retrievedUser = em.find(User.class, user.getId());
        System.out.println("Retrieved User: " + retrievedUser.getName());
        System.out.println("User's Address: " + retrievedUser.getAddress().getStreet() + ", " + retrievedUser.getAddress().getCity());

        // Close EntityManager and EntityManagerFactory
        em.close();
        emf.close();
    }
}