Spring Data JPA query return repeated row instead of actual data, why?

Md. Asaduzzaman :

Entity class

public class Event {

    @Id
    private String name;

    private String description;

    private Date eventDateTime;

    //getter and setter code
}

Service Class

EventService {

  @Autowired EventRepository eventRepository;

  List<Event> getEvents () {
     List<Event> events = eventRepository.findAll();

     return events;
  }
}

For sample data set: Event ('add', '', '2018-01-01 00:00:10') Event ('add', '', '2018-01-01 00:10:10') Event ('delete', '', '2018-01-01 00:20:00') Event ('edit', '', '2018-01-01 00:30:00')

JPA findAll() query return repeated rows:

Event ('add', '', '2018-01-01 00:00:10') Event ('add', '', '2018-01-01 00:00:10') Event ('add', '', '2018-01-01 00:00:10') Event ('add', '', '2018-01-01 00:00:10')

Md. Asaduzzaman :

To avoid repeated (duplicate) data, we have to ensure there is a unique key and that will be annotated by @Id. In this example, name it self is not unique, that's why the result show duplicate data. eventDateTime is better choice as unique field.

public class Event {

    private String name;

    private String description;

    @Id
    private Date eventDateTime;

    //getter and setter code
}

Or, we can define a composite unique key with name and eventDateTime.

public class CompositeKey implements Serializable { 

    private String name;

    private Date eventDateTime;
}

Then, annotated Event class with @IdClass(CopositeKey.class) and both name and eventDateTime field with @Id

 @IdClass(CopositeKey.class)
 public class Event {
        @Id
        private String name;

        private String description;

        @Id
        private Date eventDateTime;

        //getter and setter code
    }