querydsl從元組獲取列

Question

我創建了返回建築物ID和該建築物中公寓數量的查詢。 如何從該元組中獲得具有最大數量的建築物？ 除了遍歷整個列表。

JPAQuery<Tuple> query2 = new JPAQuery(entityManager);
QBuildingEntity building = QBuildingEntity.buildingEntity;
QApartmentEntity apartment = QApartmentEntity.apartmentEntity;
query2 = query2.select(apartment.count(), apartment.building.id).from(apartment).where(apartment.status.lower().eq("free"))
                .groupBy(apartment.building);

以下是建築物和公寓實體：

public class BuildingEntity extends AbstractEntity implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    Long id;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "building", cascade = CascadeType.ALL, orphanRemoval = true)
    Set<ApartmentEntity> apartments = new HashSet<>();
}

public class ApartmentEntity extends AbstractEntity implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    Long id;
    @Column(name = "STATUS", nullable = false, length = 50)
    String status;

    @ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH})
    @JoinColumn(name = "BUILDING_ID")
    BuildingEntity building;
}

Answer 1

您可以通過apartment.count()降序對查詢進行排序，然后選擇第一個結果。 就像是：

query2.select(apartment.count(), apartment.building.id)
      .from(apartment)
      .where(apartment.status.lower().eq("free"))
      .groupBy(apartment.building)
      .orderBy(apartment.count().desc())
      .limit(1L);