具有單向關系的標准 API

Question

我有三個實體。 我需要構建標准 API 如果唯一用戶將超過 userCount 變量，我可以在其中進行 select 項目。

@Entity
@Table(name = "client")
public class Client {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Getter @Setter private Long id;
}

@Entity
@Table(name = "session")
public class Session {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Getter @Setter private Long id;

    @ManyToOne
    @JoinColumn(name = "client_id", referencedColumnName = "id")
    @Getter @Setter private Client client;

    @ManyToOne
    @JoinColumn(name = "project_id", referencedColumnName = "id")
    @Getter @Setter private Project project;
}

@Entity
@Table(name = "project")
public class Project {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Getter @Setter private Long id;
}

我想要 select 所有項目，其中唯一用戶> = userCount。 我在 jpql 中構造查詢

@Query("select p from Project p where (select distinct count(cli.id) from Client as cli 
join Session sess on sess.client = cli 
join Project as proj on proj = sess.project 
where proj.id = p.id) >= :userCount")

我寫了標准：

        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<Project> cq = cb.createQuery(Project.class);
        Root<Project> projectRoot = cq.from(Project.class);

        List<Predicate> predicates = new ArrayList<>();

        Subquery<Long> sub = cq.subquery(Long.class);
        Root<Client> subRoot = sub.from(Client.class);

        Join<Client, Session> sessionClientJoin = subRoot.join("sessions");
        Join<Session, Project> sessionProjectJoin = sessionClientJoin.join("project");

        sub.select(cb.count(subRoot.get("id"))).distinct(true);
        sub.where(cb.equal(projectRoot.get("id"), sessionProjectJoin.get("id")));

        predicates.add(cb.greaterThanOrEqualTo(sub, DefaultParamsHolder.NUMBER_OF_USERS));
        cq.select(projectRoot);
        cq.where(predicates.toArray(new Predicate[0]));
        List<Project> project = em.createQuery(cq).getResultList();

這工作正常，但此標准需要客戶端 class 中的會話。

@Entity
@Table(name = "client")
public class Client {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Getter @Setter private Long id;

    @OneToMany(mappedBy = "client", fetch = FetchType.LAZY)
    private List<Session> sessions;
}

這對我很不利。 我需要在客戶端 class 中構建沒有會話的標准 API。 我試過這個：

        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<Project> cq = cb.createQuery(Project.class);
        Root<Project> projectRoot = cq.from(Project.class);

        List<Predicate> predicates = new ArrayList<>();

        Subquery<Long> sub = cq.subquery(Long.class);
        Root<Client> subRoot = sub.from(Client.class);

        Join<Session, Client> sessionClientJoin = subRoot.join("client");
        Join<Session, Project> sessionProjectJoin = sessionClientJoin.join("project");

        sub.select(cb.count(subRoot.get("id"))).distinct(true);
        sub.where(cb.equal(projectRoot.get("id"), sessionProjectJoin.get("id")));

        predicates.add(cb.greaterThanOrEqualTo(sub, DefaultParamsHolder.NUMBER_OF_USERS));
        cq.select(projectRoot);
        cq.where(predicates.toArray(new Predicate[0]));
        List<Project> project = em.createQuery(cq).getResultList();

這行不通。

java.lang.IllegalArgumentException: Unable to locate Attribute  with the the given name [client] on this ManagedType [com.engage.domain.model.statisctic.Client]

如果沒有客戶端 class 中的會話，我怎么能做到這一點？

Answer 1

你有

Root<Client> subRoot = sub.from(Client.class);
Join<Session, Client> sessionClientJoin = subRoot.join("client");

此連接表示“加入綁定到客戶端屬性的客戶端 class 實體”。 Client沒有屬性client - 這就是錯誤所說的。

也許您想加入與客戶的會話

   Join<Client, Session> sessionClientJoin = subRoot.join("sessions");

我的建議是開始使用 static 生成的元模型。 這將保證編譯時屬性的有效性和類型安全。

https://www.baeldung.com/hibernate-criteria-queries-metamodel