[英]Query for tables with @ManyToMany relation(Hibernate)
我使用 Hibernate 重寫了我的 SpringMVC 應用程序。我嘗試通過使用 SQL 查詢(在我開始使用 Hibernate 重寫它之前)查詢通過組的 id 為學生組選擇講座。這個查詢是:
"SELECT * FROM lectures WHERE id IN (SELECT lecture_id FROM lectures_groups WHERE group_id =?) ORDER BY date_of_lecture"
我有 Lecture 和 Group etities:
@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
}
我嘗試了類似的東西:
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 那么我該怎么做呢?
在hql
查詢中,您需要在查詢中提供entity
的名稱而不是表名。 因此,在您的情況下,您應該在查詢中將lectures
替換為Lecture
。
List<Lecture> lectures = session.createQuery("select l from Lecture l join l.groups g where g.id=:groupId")
.setParameter("groupId", group.getId())
.list();
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