使用 spring 引导的一对多单向关系

Question

I have an entity class called user with the following code:

@Table(name="user")
public class User {

    //one-to-many relationship with borrowed books
    
    @OneToMany(mappedBy="user", cascade = CascadeType.ALL)
    @JoinColumn(name="user_id")
    
    private List<BorrowedBooks> borrowedBooks;
    
    
    


    //define fields
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id")
    private Integer id;
    
    @Column(name="first_name")
    private String firstName;

    
    // getters and setters go here

    //this is the method used to add the borrowed books
      public void addBorrowedBook(BorrowedBooks borrowedbook) {
        if(borrowedBooks==null) {
            borrowedBooks = new ArrayList<>();
        }
        borrowedBooks.add(borrowedbook);
    }

below is the code for books table

@Entity
@Table(name="books")
public class Books {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id")
    private Integer Id; // autogenerated unique values.
    
    @Column(name="title")
    private String title;
    @Column(name="genre")
//getters and setters go here

Below is the code for borrowed books entity class:

   public class BorrowedBooks {

    
    @Id
    @GeneratedValue(strategy= GenerationType.AUTO)
    @Column(name="id")
    private Integer id;
    
    @Column(name="bookName")
    private String bookName;
    @Column(name="genre")
    private String genre ;
    //getters and setters goes here
}

The hibernate code for adding the borrowed book code is as follows:

User newUser = new User(1,"john doe") //the values are userId,first_name
newUser.addBorrowedBook(new BorrowedBooks(1,"love to code", "computer science")); //values are id,book name, genre
session.save(newUser) // this saves the user along with the borrowed book details with userId as foreignKey into the database

I am trying to implement this code using spring rest controller

@RestController
@RequestMapping("/base path goes here")
public class BorrowedBooksRestController {
private BorrowedBooksService borrowedBooksService;
    
    public BorrowedBooksRestController(BorrowedBooksService borrowedBooksService) {
        this.borrowedBooksService = borrowedBooksService;
    }
@PostMapping("/users")
    public void addBorrowedBooks(@RequestBody User theUser) {
                //this allows me to access the user id which is the foreign key for the borrowedBooks entity class but I need to access the borrowedBooks details as well such as bookName, genre etc. 
How do I send values from both user and borrowed books entity class.
   borrowedBooksService.save()//here we add the borrowedBook object to save in the database

    }

As seen from the code above, I can access the userId from the frontend, but how am I to replicate the object creation seen in the hibernate code here? I need to access the bookName and genre from the frontend along with the user id. I am using postman as a rest client for the time being.

Answer 1

For your task you need both userId and bookId from frontend to pass to addBorrowedBook controller.If you have bookId, because the bookId is the primary key of book entity you can uniquely identify the book. No need of knowing book genre or name. Therefore from bookId you can fetch data from boook table and create book object. Then you can add that book object to the user object borrowed book List and save/update as in the sample code.

Otherwise if your table not contain book details in your table you do not have other choise rather than passing book genre and etc... from frontend.

To pass book info well as userId do this way.

    @postMapping('/user')
    public void addBorrowedBook(@RequestParam int userId, @RequestParam String genre, @RequestParam Stringbookname)