我需要一个多对多的hibernate映射，需要3个连接。我试图找到一个没有中间实体的解决方案，比如讲师课程。
在我的数据库中，讲师和课程表之间存在多对多的关系。一门课程可以由几个讲师讲授，而一个讲师可以讲授几个课程。
我手头有课程。然而，我需要把课程分配给讲师。当我分配课程时，我也会存储该课程的容量。
我的数据库关系图：
我用冬眠和Spring。当课程分配给任何讲师时，我需要一个hibernate映射。我需要向容量字段添加值。
我的讲师映射：
@Entity
@Table(name="LECTURER")
public class Lecturer {
@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="LECTURER_ID_SEQ")
@SequenceGenerator(name="LECTURER_ID_SEQ", sequenceName="LECTURER_ID_SEQ")
private Long Id;
@Column(name="NAME")
private String name;
@Column(name="SURNAME")
private String surname;
@Column(name="EMAIL")
private String email;
@Column(name="USERNAME")
private String username;
@Column(name="PASSWORD")
private String Password;
@ManyToMany
@JoinTable(
name="LECTURER_COURSE",
joinColumns=@JoinColumn(name="LECTURER_ID"),
inverseJoinColumns=@JoinColumn(name="COURSE_ID")
)
private List<Course> courses;
//getters - setters
}
我的课程地图：
@Entity
@Table(name="COURSE")
public class Course {
@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="COURSE_ID_SEQ")
@SequenceGenerator(name="COURSE_ID_SEQ", sequenceName="COURSE_ID_SEQ")
private Long id;
@Column(name="NAME")
private String name;
@Column(name="CODE")
private String code;
}
知道如何解决我的问题吗？
您需要使用@EmbeddedId和@Embedable注解来解决这个问题：
讲师课程:
@Entity
@Table(name="LECTURER")
public class Lecturer {
@OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.lecturer", cascade=CascadeType.ALL)
Set<LecturerCourse> lecturerCourses == new HashSet<LecturerCourse>();
//all others properties Setters and getters are less relevant.
}
课程类别：
@Entity
@Table(name="COURSE")
public class Course {
@OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.course", cascade=CascadeType.ALL)
Set<LecturerCourse> lecturerCourses == new HashSet<LecturerCourse>();
//all others properties Setters and getters are less relevant.
}
讲师课程类：
@Entity
@Table(name = "lecturer_course")
@AssociationOverrides({
@AssociationOverride(name = "pk.lecturer",
joinColumns = @JoinColumn(name = "LECTURER_ID")),
@AssociationOverride(name = "pk.course",
joinColumns = @JoinColumn(name = "COURSE_ID")) })
public class LecturerCourse {
private LecturerCourseID pk = new LecturerCourseID();
@Column(name = "CAPACITY", nullable = false, length = 10)
private String capacity;
@EmbeddedId
public LecturerCourseID getPk() {
return pk;
}
}
现在的主键：
@Embeddable
public class LecturerCourseID implements java.io.Serializable {
private Lecturer lecturer;
private Course course;
@ManyToOne
public Stock getLecturer() {
return lecturer;
}
public void setLecturer(Lecturer lecturer) {
this.lecturer= lecturer;
}
@ManyToOne
public Course getCourse() {
return course;
}
public void setCourse(Course course) {
this.course= course;
}
}
现在你的主应该像这样：
Lecturer lecturer1 = new Lecturer();
Course math = new Course();
LecturerCourse lecturer1math = new LecturerCourse();
lecturer1math.setCapacity("capacity");
lecturer1math.setLecturer(lecturer1);
lecturer1math.setCourse(math);
lecturer1.getLecturerCourses().add(lecturer1math);
//saving object
session.save(lecturer1);
您需要确保标记为@Embedable的类应该实现Serializable标记接口。
希望有帮助。
