Group by and reduce to a json list-CodePudding

Hi have native sql query which returns List interface class with 3 fields

Trying to find a clean efficient way to do this to reduce to sub-list

Appreciate help

Thanks

SQL query List findResponse();

Response class

public interface Response {
    Long getId();

    String getSData();

    String getSName();
}

The query result converted to json looks as

[
{"id":1,"sData":"UK,FR","sName":"X},
{"id":2,"sData":"UK,FR","sName":"Y"},
{"id":4,"sData":"EU","sName":"X"},
{"id":4,"sData":"Others","sName":"O"}
]

Expected Output For ex for id=4

{
    “subData” :
          [
              {
                 “sData”: “X”,
                 “sName”: “EU”
              },
              {
                 "sName": "O",
                 "sData": "Others"
              }
          ]
    }

I can create another class if needed

@Data
public class NewResponse {

    public Long id;
    public List<subData> subDataList;
}

CodePudding user response：

I would start off by grouping to a map:

Map<Long> grouped = responses.stream()
        .collect(groupingBy(Response::getId,
                mapping(r -> new SubData(r.getSData(), r.getSName()), toList())));

Then you can stream the Map entries to convert them to NewResponses:

List<NewResponse> mapped = grouped.entrySet()
        .stream()
        .map(e -> new NewResponse(e.getKey(), e.getValue()))
        .collect(toList());

Feel free to chain the operations if you don't want the extra grouped variable.