Hibernate/JPA中非映射实体ID的灵活引用与查询策略

// Parent 实体
@Entity
@Table(name = "parent_entity")
public class Parent {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    // Getter, Setter, Constructors...
}

// ChildLog 实体
@Entity
@Table(name = "child_log_entity")
public class ChildLog {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    // 存储 Parent 的 ID，但没有 @ManyToOne 映射
    @Column(name = "parent_id")
    private Long parentId;

    private String childNameSnapshot; // 子实体名称快照
    private Instant recordStartTime;
    private Instant recordEndTime;

    // Getter, Setter, Constructors...
}

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

public class QueryService {

    private EntityManager entityManager; // 假设通过依赖注入获取

    public QueryService(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    /**
     * 查询某个Parent实体及其关联的ChildLog记录
     * @param parentName 父实体名称
     * @return 包含Parent和ChildLog的Object数组列表
     */
    public List<Object[]> findParentAndChildLogsByParentName(String parentName) {
        String hql = "SELECT p, cl " +
                     "FROM Parent p " +
                     "JOIN ChildLog cl ON p.id = cl.parentId " + // 核心：使用JOIN...ON连接
                     "WHERE p.name = :parentName";

        TypedQuery<Object[]> query = entityManager.createQuery(hql, Object[].class);
        query.setParameter("parentName", parentName);
        return query.getResultList();
    }

    /**
     * 仅查询某个Parent ID下的所有ChildLog记录
     * @param parentId 父实体ID
     * @return 匹配的ChildLog实体列表
     */
    public List<ChildLog> findChildLogsByParentId(Long parentId) {
        String hql = "SELECT cl " +
                     "FROM ChildLog cl " +
                     "WHERE cl.parentId = :parentId"; // 直接通过parentId字段查询

        TypedQuery<ChildLog> query = entityManager.createQuery(hql, ChildLog.class);
        query.setParameter("parentId", parentId);
        return query.getResultList();
    }
}