Why do I have to input ID (PK) - problem with auto generating ID

Question

I'm creating renting a book method in my book rental. It looks like this:

@PostMapping("/book")
public void purchaseBook(@RequestParam("userID") int userID, @RequestParam("bookID") int bookID) {
    bookRentalService.rentBook(userID, bookID);
}

After inputting userID and bookID, book if is available, it is added to BookRentalDB.

Relations between tables I made like this:

Entity of rentals:

package bookrental.model.book;

import bookrental.model.account.User;
import lombok.*;

import javax.persistence.*;

@Entity
@Getter
@Setter
@EqualsAndHashCode
@AllArgsConstructor
@NoArgsConstructor
public class BookRentals {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    @OneToOne
    private Book book;
    @OneToOne
    private User user;
}

I've got problem with creating object of this entity(BookRentals) in Service. It needs to contain object of Book and object of User. I've created constructors for this object with only bookID for Book and userID for User. In prepareBookToRent Im asked to put ID of BookRentals class, too. In that case I can not to create object of it. Should it not be generated automatically? What should I do to make it work.

package bookrental.service.book;

import bookrental.model.account.User;
import bookrental.model.book.Book;
import bookrental.model.book.BookRentals;
import bookrental.repository.book.BookRepository;
import bookrental.repository.book.BookRentalsRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class BookRentalService {

    private final BookRepository bookRepository;
    private final BookRentalsRepository bookRentalsRepository;

    @Autowired
    public BookRentalService(BookRepository bookRepository, BookRentalsRepository bookRentalsRepository) {
        this.bookRepository = bookRepository;
        this.bookRentalsRepository = bookRentalsRepository;
    }

    public void rentBook(int userID, int bookID) {
        if (bookRepository.doesBookExistsWithGivenID(bookID)) {
            Book bookToRent = bookRepository.findOne(bookID);
            if (bookToRent.isAvailable()) {
                updateBookAvailabilityAndSaveToDb(bookToRent);
                BookRentals preparedBookToRent = prepareBookToRent(userID, bookID);
                bookRentalsRepository.save(preparedBookToRent);
            } else {
                throw new IllegalArgumentException("Book is no available");
            }
        }
        throw new IllegalArgumentException("Book does not exist!");
    }


    private BookRentals prepareBookToRent(int userID, int bookID) {
        return new BookRentals(new Book(bookID),new User(userID)); // here im asked to input ID, too
    }

    private void updateBookAvailabilityAndSaveToDb(Book bookToRent) {
        bookToRent.setAvailable(false);
        bookRepository.save(bookToRent);
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.book.rental.piotrek</groupId>
    <artifactId>BookRental</artifactId>
    <version>1.0-SNAPSHOT</version>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>8</source>
                    <target>8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.9.RELEASE</version>
    </parent>



    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.16.22</version>
        </dependency>
    </dependencies>

</project>

Staktrace

C:\Users\Admin\IdeaProjects\BookRental\src\main\java\bookrental\service\book\BookRentalService.java
Error:(39, 16) java: no suitable constructor found for BookRentals(bookrental.model.book.Book,bookrental.model.account.User)
    constructor bookrental.model.book.BookRentals.BookRentals(int,bookrental.model.book.Book,bookrental.model.account.User) is not applicable
      (actual and formal argument lists differ in length)
    constructor bookrental.model.book.BookRentals.BookRentals() is not applicable
      (actual and formal argument lists differ in length)

As I said above, this is it:

Answer 1

You're wrong, you created all args contstructor. You have 3 attributes. This means, you have all args constructor with 3 arguments not 2.

Just create custom constructor.

public BookRentals (Book book, User user) {
// logic
}

ps: why not possible to exclude some parameter from all args: Java Lombok: Omitting one field in @AllArgsConstructor?

upd: comments are stating something crazy. So, if you got one to one, use annotation on entity directly. If you got many to many, consider OneToMany, as having multiple users renting same book is not realistic.

refer to this for table design: How to implement one-to-one, one-to-many and many-to-many relationships while designing tables?