How to check spring boot post API if it is available in the database

Question

**Controller**
package com.example.curd.curdtesting.controller;

import com.example.curd.curdtesting.entity.Book;
import com.example.curd.curdtesting.service.BookServiceImpl;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
public class Controller {
    @Autowired
    BookServiceImpl bookService;
  
    @PostMapping("/addProducts")
    public List<Book> addProducts(@RequestBody List<Book> book) {
        return bookService.insertBook(book);
    }
}

**Entity class**
package com.example.curd.curdtesting.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Data
@AllArgsConstructor
@NoArgsConstructor
@Table
public class Book {
    @Id
    @GeneratedValue
    private int id;
    private String name;
    private String description;

}

**Service class**

package com.example.curd.curdtesting.service;

import com.example.curd.curdtesting.entity.Book;
import com.example.curd.curdtesting.repository.BookRepo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Optional;

@Service
public class BookServiceImpl {
    @Autowired
    BookRepo bookRepo;

     public List<Book> insertBook(List<Book> book) {

       return bookRepo.saveAll(book);
    }
}

**Repository**

package com.example.curd.curdtesting.repository;
import com.example.curd.curdtesting.entity.Book;
import org.springframework.data.jpa.repository.JpaRepository;

import java.util.List;

public interface BookRepo extends JpaRepository<Book, Integer> {
    public List<Book> findBookByName(String name);
}

Once the item is received from user in json format. I want to check if the book with same name is already in my database if so, i want to output duplicate no possible. As I receive book object from json but how to check in service layer if the book with the name is present in database. Can anyone please help me as I am new to spring boot.

Answer 1

Your service layer is the place to set your business rules and you can do as follow :

1. Create a custom exception to handle your logic, for example : RecordExistsException
2. Create a RestControllerAdvice to handle your exception. In this class, you can return the message thrown by your exception.
3. Check if your record exists and throw a RecordExistsException when your findBookByName(String name) returns an already existing book.

The service class will look something like this:

@Service
public class BookServiceImpl {
    @Autowired
    BookRepo bookRepo;

     public List<Book> insertBook(Book book) {
       if(!bookRepo.findByName(book.getName()).isEmpty()) {
           throw new RecordExistsException("The book " + book.getName() + " already exists !!!")
       }
       return bookRepo.saveAll(book);
    }
}