优化JPA查询性能：利用Tuple和Java Stream高效处理复杂关联数据

public class ParentDto {
    private String id;
    private String name;
    private Collection<String> childIds;

    public ParentDto(String id, String name, Collection<String> childIds) {
        this.id = id;
        this.name = name;
        this.childIds = childIds;
    }

    // Getters and Setters
    public String getId() { return id; }
    public String getName() { return name; }
    public Collection<String> getChildIds() { return childIds; }

    public void setId(String id) { this.id = id; }
    public void setName(String name) { this.name = name; }
    public void setChildIds(Collection<String> childIds) { this.childIds = childIds; }
}

import javax.persistence.EntityManager;
import javax.persistence.Tuple;
import javax.persistence.TypedQuery;
import java.util.List;

// ...

public List<Tuple> findParentAndChildIds(EntityManager em) {
    // 假设 Parent 实体有 id 和 name 字段
    // 假设 Child 实体有 id 字段，并通过 parent 字段关联 Parent 实体
    String jpql = "SELECT p.id AS parentId, p.name AS parentName, c.id AS childId " +
                  "FROM Parent p JOIN p.children c"; // 或者 JOIN Child c ON c.parent = p

    TypedQuery<Tuple> query = em.createQuery(jpql, Tuple.class);
    return query.getResultList();
}

import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

// ...

public List<ParentDto> mapTuplesToParentDtos(List<Tuple> tuples) {
    if (tuples == null || tuples.isEmpty()) {
        return List.of();
    }

    // 使用 Collectors.groupingBy 进行分组，然后使用 Collectors.mapping 收集子ID
    Map<String, ParentDto> parentDtoMap = tuples.stream()
        .collect(Collectors.groupingBy(
            tuple -> tuple.get("parentId", String.class), // 根据 parentId 分组
            Collectors.collectingAndThen(
                Collectors.toList(), // 收集每个 parentId 对应的所有 Tuple
                groupedTuples -> {
                    // 取第一个 Tuple 获取父实体信息（因为父实体信息在同一组内是重复的）
                    Tuple firstTuple = groupedTuples.get(0);
                    String parentId = firstTuple.get("parentId", String.class);
                    String parentName = firstTuple.get("parentName", String.class);

                    // 收集所有子ID
                    List<String> childIds = groupedTuples.stream()
                        .map(tuple -> tuple.get("childId", String.class))
                        .distinct() // 确保子ID不重复，如果 JOIN 方式可能导致重复
                        .collect(Collectors.toList());

                    return new ParentDto(parentId, parentName, childIds);
                }
            )
        ));

    // 将 Map 的值转换为 List
    return new java.util.ArrayList<>(parentDtoMap.values());
}