联合外键作主键 @EmbeddwdId

package com.dlnu.model;

import java.io.Serializable;

import javax.persistence.Embeddable;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
@Embeddable
public class Name implements Serializable {

private static final long serialVersionUID = 1L;

private Course course;

private Student student;

public Name() {
}

public Name(Course course, Student student) {
this.course = course;
this.student = student;

}

@ManyToOne
@JoinColumn(name = "courseId", referencedColumnName = "cno",nullable=true)
public Course getCourse() {
return course;
}
@ManyToOne
@JoinColumn(name = "studentId", referencedColumnName = "sno")
public Student getStudent() {
return student;
}

public void setStudent(Student student) {
this.student = student;
}

public void setCourse(Course course) {
this.course = course;
}

public boolean equals(Object obj) {

if (this == obj) {
return true;
}
if (obj.getClass() == Name.class) {
Name target = (Name) obj;
if (target.getCourse().equals(course)
&& target.getStudent().equals(student)) {
return true;
}
}
return false;
}

public int hashCode() {

return course.hashCode() + student.hashCode() * 17;
}

}

package com.dlnu.model;

import javax.persistence.EmbeddedId;
import javax.persistence.Entity;

@Entity
public class SC {

private Name name;

private Double grade;

public Double getGrade() {
return grade;
}

@EmbeddedId
public Name getName() {
return name;
}
public void setGrade(Double grade) {
this.grade = grade;
}
public void setName(Name name) {
this.name = name;
}

}