JPA Returning Empty Set When Should Be Empty Optional<>

Question

I have the following two entities:

@Entity
@Table(name = "organization")
@AllArgsConstructor
@NoArgsConstructor
@Data
@Builder
public class Organization {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    Long id;

    @Column(name = "name")
    String name;

    @OneToMany(mappedBy = "organization")
    Set<Team> teams;
    
}

@Entity
@Table(name = "team")
@AllArgsConstructor
@NoArgsConstructor
@Data
@Builder
public class Team {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    Long id;

    @Column(name = "name")
    String name;

    @Column(name = "description")
    String description;

    @ManyToOne
    @JoinColumn(name="organization_id", nullable=false)
    Organization organization;
    
}

And the following two repositories for those entities

@Repository
public interface OrganizationRepo extends CrudRepository<Organization, Long> {
    
}

@Repository
public interface TeamRepo extends CrudRepository<Team, Long> {

    Optional<Set<Team>> findByOrganizationId(Long organizationId);

    Optional<Team> findByOrganizationIdAndTeamId(Long organizationId, Long teamId);
    
}

I then try to use the findByOrganizationId(..) method with an organizationId which does not exist, and want it to return an empty optional, but instead I get a HashSet<> with 0 items? Is there a way that I can accomplish this functionality with a JPA method?

    @Autowired
    TeamRepo repository;

    @ResponseBody
    @GetMapping(value = "/api/v1/organization/{organizationId}/team")
    ResponseEntity<Iterable<Team>> index(@PathVariable Long organizationId) {

        Optional<Set<Team>> result = repository.findByOrganizationId(organizationId);

        if(result.isPresent()) {

            return new ResponseEntity<>(result.get(), HttpStatus.OK);

        } else {

            return new ResponseEntity<>(HttpStatus.NOT_FOUND);

        }

    }

Edit: As Organization to Teams is a OneToMany relationship, it is reasonable that if there is no Organization, it should return an empty Optional<>, but if there is an Organization with 0 or more teams, it should return an Optional<> with a Set<> of zero or more teams.

Granit Krasniqi · Accepted Answer · 2021-12-17 19:20:32Z

3

When you use collections as results you don't need to wrap it in Optional, you can check the collection directly with isEmpty() method:

@Repository
public interface TeamRepo extends CrudRepository<Team, Long> {

    Set<Team> findByOrganizationId(Long organizationId);

    Optional<Team> findByOrganizationIdAndTeamId(Long organizationId, Long teamId);
    
}




@Autowired
TeamRepo repository;

@ResponseBody
@GetMapping(value = "/api/v1/organization/{organizationId}/team")
ResponseEntity<Iterable<Team>> index(@PathVariable Long organizationId) {

    Set<Team> result = repository.findByOrganizationId(organizationId);

    if(!result.isEmpty()) {

        return new ResponseEntity<>(result, HttpStatus.OK);

    } else {

        return new ResponseEntity<>(HttpStatus.NOT_FOUND);

    }

}

Effective Java book states that: Container types, including collections, maps, streams, arrays, and optionals should not be wrapped in optionals.

answered Dec 17, 2021 at 19:20

Granit Krasniqi

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5 Comments

Kirkland Over a year ago

I was about to say "but then why does it do it with the original findById(..) method, but then I checked, and it doesn't. So good point, however I want it is representing a OneToMany relationship, and so therefore if there isn't an organization, return empty optional, but if there is an organization return a set with 0 or more items.

Granit Krasniqi Over a year ago

based on my understanding you are trying to check if the organization exists with that id before trying to find the Teams of that organization. If this is the case then you need to inject @Autowired OrganizationRepo organizationRepo; in your controller and then call organizationRepo.findById(organizationId) that returns Optional, if that is empty return return new ResponseEntity<>(HttpStatus.NOT_FOUND); otherwise return the result from repository.findByOrganizationId(organizationId)

Kirkland Over a year ago

Right, I know that is a way of doing it I was just wondering if there was a cleaner way of doing it with a single query using JPA Repository Methods.

Granit Krasniqi Over a year ago

I don't think there is a cleaner approach, you need to do these two calls.

Kirkland Over a year ago

Ok, cool. I'm going to leave the question up for the weekend and if no one else comes back with any ideas I'll mark this as the answer. Thanks for your quick reply!

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