problem in creating api function to save the data in the repository?

[niraj28]

In Order.java
@manytomany(cascade=CascadeType.ALL)
@jointable(name = "order1_books" ,joinColumns = { @joincolumn(name ="orderid")},
inverseJoinColumns = { @joincolumn(name ="bookid")}
)
private List books;

In Book.java
@manytomany(targetEntity=Order.class,mappedBy="books", cascade = CascadeType.ALL, fetch=FetchType.EAGER)

private List<Order> orders;	

in controller how to write the function for save the given conditions
@RestController
public class BookProjectApplication {

public static void main(String[] args) {
	SpringApplication.run(BookProjectApplication.class, args);
}

@Autowired
OrderRepository orderrepository ;

@Autowired
BookRepository bookrepository;



 @RequestMapping(method=RequestMethod.POST, value="/manyorder/order/{orderid}")
    public void add(@RequestBody  List<Order> order, @PathVariable String orderid){
	 
	 for(int i=0;i<order.size();i++) {
                   orderrepository.save((new Order(orderid,"","",0,0))); 
                  Optional<Book> book=bookrepository.findById(order.get(i).getBookid());
    //              order.get(i).addBook(book);
 	   ///    bookrepository.save((new Book(bkid,"","","",0)));	
 	       //bookrepository.
    	 }	    
       
    }

}

Any good resource to understand the way to write api for the ManyToMany releation is also appreciated..