How to return list of specific fields in query Java Spring Mongo Repository?

Question

I use Java spring and MongoDB repository in my project.

Here is DTO definition:

@Document(collection = "Info")
public class Info  {

  String id,
  Integer count,
  String type
  …
}

I need to return from the query a list of IDs where the count field not zero and type filed has 'binary' text.

Here how I try to implement it:

@Query(value="{ 'count' : 0, 'type' : 'binary' }", fields="{ 'id' : 1 }")
List<String> getInfo();

I get this result from query above:

0={"_id": {"$oid": "5eb97a8139d4c62be4d90e4c"}}
1={"_id": {"$oid": "3ec97a8127d4c60cb4d90e9e"}}

And I expect this result:

{"5eb97a8139d4c62be4d90e4c", "3ec97a8127d4c60cb4d90e9e"}

So as you can see I expect to get a list of id strings from the query above.

Any idea what should I change in the query above to get the expected list of ids results?

Answer 1

No, that's impossible what you are thinking.

Reason : MongoDB can only return JSON Document. You can include the fields that you want to be there.

This suggestion that you can follow :

DTO Definition :

@Document(collection = "Info")
public class Info  {

  @Id
  private String id;
  
  private Integer count;
  
  private String type;
  
  // other fields and getters and setters
}

Sample Repository :

public interface InfoRepository extends MongoRepository<Info, String> {

   @Query(value="{ 'count' : 0, 'type' : 'binary' }", fields="{ 'id' : 1 }")
   List<Info> getInfo();
 
}

Sample Service class :

@Service
public class InfoService {

   @Autowired 
   private InfoRepository infoRepository;

   public List<String> getIds() {
   
      return infoRepository.getInfo()
                      .stream()
                      .map(Info::getId)
                      .collect(Collectors.toList());    

   }

}