JPA Repository Examples

  

Example 1: One-to-One Relationship

Scenario: Managing a one-to-one relationship between Person and Passport.

Entities: Person and Passport

Person.java

import javax.persistence.*;

@Entity
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @OneToOne(mappedBy = "person", cascade = CascadeType.ALL)
    private Passport passport;

    // Constructors, getters, setters
}

Passport.java

import javax.persistence.*;

@Entity
public class Passport {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String number;
    
    @OneToOne
    @JoinColumn(name = "person_id")
    private Person person;

    // Constructors, getters, setters
}

PersonRepository.java

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

public interface PersonRepository extends JpaRepository<Person, Long> {
}

Usage in Application:

@Service
public class PersonService {
    
    @Autowired
    private PersonRepository personRepository;

    @Transactional
    public void savePersonWithPassport() {
        Person person = new Person("John");
        Passport passport = new Passport("ABC123");
        
        person.setPassport(passport);
        passport.setPerson(person);
        
        personRepository.save(person);
    }
}

Example 2: One-to-Many Relationship

Scenario: Managing a one-to-many relationship between Author and Book.

Entities: Author and Book

Author.java

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

@Entity
public class Author {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @OneToMany(mappedBy = "author", cascade = CascadeType.ALL)
    private List<Book> books;

    // Constructors, getters, setters
}

Book.java

import javax.persistence.*;

@Entity
public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String title;
    
    @ManyToOne
    @JoinColumn(name = "author_id")
    private Author author;

    // Constructors, getters, setters
}

AuthorRepository.java

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

public interface AuthorRepository extends JpaRepository<Author, Long> {
}

Usage in Application:

@Service
public class AuthorService {
    
    @Autowired
    private AuthorRepository authorRepository;

    @Transactional
    public void saveAuthorWithBooks() {
        Author author = new Author("Jane Austen");
        Book book1 = new Book("Pride and Prejudice");
        Book book2 = new Book("Sense and Sensibility");
        
        author.getBooks().add(book1);
        author.getBooks().add(book2);
        
        book1.setAuthor(author);
        book2.setAuthor(author);
        
        authorRepository.save(author);
    }
}

Example 3: Many-to-Many Relationship

Scenario: Managing a many-to-many relationship between Student and Course.

Entities: Student and Course

Student.java

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

@Entity
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @ManyToMany
    @JoinTable(name = "student_course",
            joinColumns = @JoinColumn(name = "student_id"),
            inverseJoinColumns = @JoinColumn(name = "course_id"))
    private List<Course> courses;

    // Constructors, getters, setters
}

Course.java

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

@Entity
public class Course {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @ManyToMany(mappedBy = "courses")
    private List<Student> students;

    // Constructors, getters, setters
}

StudentRepository.java

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

public interface StudentRepository extends JpaRepository<Student, Long> {
}

Usage in Application:

@Service
public class StudentService {
    
    @Autowired
    private StudentRepository studentRepository;

    @Transactional
    public void enrollStudentsInCourses() {
        Student student1 = new Student("John");
        Student student2 = new Student("Jane");
        
        Course course1 = new Course("Java Programming");
        Course course2 = new Course("Database Management");
        
        student1.getCourses().add(course1);
        student1.getCourses().add(course2);
        
        student2.getCourses().add(course1);
        
        course1.getStudents().add(student1);
        course1.getStudents().add(student2);
        
        course2.getStudents().add(student1);
        
        studentRepository.save(student1);
        studentRepository.save(student2);
    }
}

Example 4: Many-to-One Relationship

Scenario: Managing a many-to-one relationship between Order and Customer.

Entities: Order and Customer

Order.java

import javax.persistence.*;

@Entity
public class Order {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String orderNumber;
    
    @ManyToOne
    @JoinColumn(name = "customer_id")
    private Customer customer;

    // Constructors, getters, setters
}

Customer.java

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

@Entity
public class Customer {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @OneToMany(mappedBy = "customer", cascade = CascadeType.ALL)
    private List<Order> orders;

    // Constructors, getters, setters
}

OrderRepository.java

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

public interface OrderRepository extends JpaRepository<Order, Long> {
}

Usage in Application:

@Service
public class OrderService {
    
    @Autowired
    private OrderRepository orderRepository;

    @Transactional
    public void createOrderForCustomer() {
        Customer customer = new Customer("John Doe");
        Order order1 = new Order("ORD001");
        Order order2 = new Order("ORD002");
        
        order1.setCustomer(customer);
        order2.setCustomer(customer);
        
        customer.getOrders().add(order1);
        customer.getOrders().add(order2);
        
        orderRepository.save(order1);
        orderRepository.save(order2);
    }
}