使用 JPA 和 QueryDSL 聚合查询结果中的子实体

public page<articledetail> findarticles(pagerequest pagerequest, user currentuser) {
    var articles = new jpaqueryfactory(entitymanager)
            .select(projections.constructor(articledetail.class,
                    article.id,
                    projections.constructor(userdetail.class,
                            user.id,
                            user.name,
                            user.username,
                            user.email,
                            user.profilepicture,
                            user.level,
                            user.position),
                    article.content,
                    article.type,
                    projections.list(projections.constructor(commentdetail.class,
                            comment.user.id,
                            comment.article.id,
                            comment.text,
                            comment.timestamp).skipnulls()).skipnulls(),
                    projections.list(projections.constructor(reactiondetail.class,
                            reaction.user.id,
                            reaction.type).skipnulls()).skipnulls(),
                    article.commentcount,
                    article.datecreated,
                    article.datelastmodified
                ))
                .from(article)
                .innerjoin(article.user, user)
                .leftjoin(article.comments, comment).on(comment.isactive.istrue())
                .leftjoin(article.reactions, reaction)
                .where(article.isactive.istrue(),
                        user.status.eq(status.active),
                        article.user.in(currentuser.getfollowing())
                                .or(article.user.eq(currentuser)))
                .offset(pagerequest.getoffset())
                .limit(pagerequest.getpagesize())
                .orderby(article.id.asc())
                .fetch();

    return new pageimpl<>(articles, pagerequest, articles.size());
}

@Entity
public class Article {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private User user;

    @OneToMany(mappedBy = "article")
    private Set<Comment> comments;

    @OneToMany(mappedBy = "article")
    private Set<Reaction> reactions;

    // Other fields like content, type, etc.
}

@Entity
public class Comment {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "article_id")
    private Article article;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private User user;

    // Other fields like text, timestamp, etc.
}

@Entity
public class Reaction {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "article_id")
    private Article article;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private User user;

    // Other fields like type, etc.
}

@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    @OneToMany(mappedBy = "user")
    private Set<Article> articles;

    // Other user fields like name, username, email, etc.
}

var articleids = jpaqueryfactory
        .select(article.id)
        .from(article)
        // conditions and joins
        .fetch();

var articles = jpaQueryFactory
        .select(article)
        .from(article)
        // Joins for comments and reactions
        .where(article.id.in(articleIds))
        .transform(groupBy(article.id).list(
            Projections.constructor(ArticleDetail.class,
                // Projection fields
            )));

return new PageImpl<>(articles, pageRequest, articles.size());