How do i check if a record already exists in table in springboot JPA?

I have a table with 4 fields. And if i inserted a record that already exists i.e all field value matches with previous record in table. How do i return record only but not insert into database ?

My model look like this:

@Entity
public class QuestionDetails {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    private String department;
    private String year;
    private String academic_year;
    private String semester;
    private String type;
    private String subject;
    private int points;
    private int unit;

// getter, setter

And Controller look this:

@Autowired
public QuestionDetailsRepository qdRepository;

 @PostMapping("/api/questionDetails")
 public QuestionDetails addQuestion(@Valid @RequestBody QuestionDetails qDetails) {

// here i want to first check if qDetails object is already present in table . 
If present i want to return that existed record instead of inserting into table.


            QuestionDetails qd = qdRepository.save(qDetails); // save only new record
    
            return qd;
        }

Using postman i send data like this:

{
 "department" : "IT",
 "year" : "2020",
 "academic_year" : "1st year",
 "semester" : "first semester",
 "type" : "objective",
 "subject" : "JAVA",
 "points" : 10,
 "unit" : 5
}

Here, i am sending data that is already present in table. So, i want to check if this record already exist? If doesn't exist insert into table otherwise return that existed record.

How do i achieve that using springboot Jpa hibernate?

Solution

Implement a select method in QuestionDetailsRepository as below. Add all the criteria which make a record unique. I am using department and year but you can use all the parameters of the QuestionDetails entity.

@Query("select qd from QuestionDetails qd where qd.department = :#{#req. department} and qd.year = :#{#req.year}")
Optional<QuestionDetails> findQuestionDetails(@Param("req") QuestionDetails req);

Ensure to implement the equals() and hashCode() in QuestionDetails class as per the unique criteria.

Your pseudo-code would look like this:

Optinal<QuestionDetails> optRecord = qdRepository.findQuestionDetails(qDetails);
if(opt.isPresent()){
  return opt.get();
}else{
  qdRepository.save(qDetails);
}