java - 使用 Spring JPA 存储库进行不同计数

Question

现在我正在计算这样的话题的观点:

Long countByViewOnTopicId(Long topicId);

这相当于 SQL 查询

select count(*) from views where topic_id = ? 

这给了我所有 View 的数量，但我需要计算唯一用户的数量。我需要相当于以下查询的 JPA:

select count(distinct user_id) from views where topic_id = ?

我可以使用 @Query注释，但我试图在项目中编写较少的自定义 SQL。如下图:

Long countDictinctUserIdByViewOnTopicId(Long topicId);

更新:
`以下条目详细信息:

@Entity
@Table(name = "views")
public class Views {

    @Id
    @GeneratedValue
    private Long id;

    @NotNull
    @Column(name = "user_id", insertable = false, updatable = false)
    private Long userId;

    @JoinColumn(name = "user_id")
    @ManyToOne
    private User user;

    @NotNull
    @Column(name = "topic_id", insertable = false, updatable = false)
    private Long topicId;

    @JoinColumn(name = "topic_id")
    @ManyToOne
    private Topic topic;

    @NotNull
    @Column(name = "action_type")
    @Enumerated(EnumType.ORDINAL)
    private ActionTypes actionType;

Getter, Setter...

Answer 1

尝试这个:

criteriaQuery.multiselect(criteriaBuilder.countDistinct(root));

https://en.wikibooks.org/wiki/Java_Persistence/Criteria