查询具有@ManyToMany 关系的表（休眠）

Question

我使用 Hibernate 重写了我的 SpringMVC 应用程序。我尝试通过使用 SQL 查询（在我开始使用 Hibernate 重写之前）进行查询以通过组的 id 为一组学生选择讲座。这个查询是：

"SELECT * FROM lectures WHERE id IN (SELECT lecture_id FROM lectures_groups WHERE group_id =?) ORDER BY date_of_lecture"

我有演讲和小组活动：

@Entity
@Table(name = "lectures")
public class Lecture {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "lectures_groups", joinColumns = @JoinColumn(name = "lecture_id"), inverseJoinColumns = @JoinColumn(name = "group_id"))
    private List<Group> groups = new ArrayList<>();
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "teacher_id")
    private Teacher teacher;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "subject_id")
    private Subject subject;
    @Column(name = "date_of_lecture")
    private LocalDateTime date;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "audience")
    private Audience audience;

    public Lecture() {

    }
//getters setters
}

和：

@Entity
@Table(name = "groups")
public class Group {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    @Column(name = "group_name")
    private String name;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "cathedra_id", referencedColumnName = "id")
    private Cathedra cathedra;
    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "lectures_groups", joinColumns = @JoinColumn(name = "group_id"), inverseJoinColumns = @JoinColumn(name = "lecture_id"))
    private List<Lecture> lectures = new ArrayList<>();

    public Group() {

    }
//getters setters
}

我试过类似的东西：

List<Lecture> lectures = session.createQuery("select l from lectures l join l.groups g where g.id=:groupId")
                .setParameter("groupId", group.getId())
                .list();

但我得到 Exception: org.hibernate.hql.internal.ast.QuerySyntaxException: Lectures is not mapped 那么我该怎么做呢？

Answer 1

在hql 查询中，您需要在查询中提供entity 的名称，而不是表名。因此，在您的情况下，您应该在查询中将 lectures 替换为 Lecture。

List<Lecture> lectures = session.createQuery("select l from Lecture l join l.groups g where g.id=:groupId")
                .setParameter("groupId", group.getId())
                .list();