QueryDsl Projection List<Dto> 쿼리 생성

QueryDsl Projections 을 사용해서 1:N 관계의 List<Object> 를 추출하는 코드를
작성해보자.

• 부모 DTO

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class ParentDto {
  private UUID id;
  private String name;

  private List<ChildDto> children = new ArrayList<>();
}

• 자식 DTO

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class ChildDto {
  private UUID id;
  private int name;
}

• 1:N DTO Projection Query 작성

List<ParentDto> results = new JPAQueryFactory(em)
  .from(parent)
  .innerJoin(child)
  .on(parent.id.eq(child.parent.id))
  .transform(
    groupBy(parent.id).list(
      Projections.fields(
        ParentDto.class,
        parent.id,
        parent.name,
        list( // `GroupByExpression` 의 static method `list()`
          Projections.fields(
            ChildDto.class,
            child.id,
            child.name
          )
        ).as("children")
      )
    )
  );