如何通过 Spring 数据计算 OneToMany 元素的项目

Question

我有一个用户实体：@Entity@Table(name = "user")@Datapublic class UserEntity extends BaseEntity {    @Column(name = "full_name")    private String fullName;    ....    @OneToMany(cascade = CascadeType.REMOVE)    @JoinTable(name = "user_post",            joinColumns = {@JoinColumn(name = "user_id")},            inverseJoinColumns = {@JoinColumn(name = "post_id")})    private Set<PostEntity> posts;    @ManyToMany    @JoinTable(name = "user_followers",            joinColumns = {@JoinColumn(name = "user_id", referencedColumnName = "id")},            inverseJoinColumns = {@JoinColumn(name = "follower_id", referencedColumnName = "id")})    private Set<UserEntity> followers = new HashSet<>();    @ManyToMany    @JoinTable(name = "user_followings",            joinColumns = {@JoinColumn(name = "user_id", referencedColumnName = "id")},            inverseJoinColumns = {@JoinColumn(name = "following_id", referencedColumnName = "id")})    private Set<UserEntity> followings = new HashSet<>();}现在我想计算一个用户的关注者。我可以获得关注者列表并使用 list.size() 但这并不好。我只想计算它们而不是整个对象。这可以通过我的 UserRepostiory 中扩展 JpaRepostiory 或本机查询的方法实现吗？

Answer 1

我建议你使用 JPQL 语法。在UserRepository你可以添加计数方法。请尝试 ：

@Query("select count(p) from User u join u.posts p where u.id = ?1")

long countPosts(Long id);

@Query("select count(f) from User u join u.followers f where u.id = ?1")

long countFollowers(Long id);

@Query("select count(f) from User u join u.followings f where u.id = ?1")

long countFollowings(Long id);