1.student，score，coure的实体关联定义如下：

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Student:

@Entity
@Table(name="tb_student")
public class Student implements Serializable {

.....
private Set<Course> courses=new HashSet<Course>();
private Set<Score> scores=new HashSet<Score>();

.....

@ManyToMany
@JoinTable(name="tb_student_course",
    joinColumns=@JoinColumn(name="student_id",referencedColumnName="id"),
    inverseJoinColumns=@JoinColumn(name="course_id",referencedColumnName="id")
    )
public Set<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
}

@OneToMany(mappedBy="student")
public Set<Score> getScores() {
return scores;
}
public void setScores(Set<Score> scores) {
this.scores = scores;
}
}

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Score:

@Entity
@Table(name="tb_score")
public class Score implements Serializable {@ManyToOne@JoinColumn(name="course_id")public Course getCourse() {return course;}public void setCourse(Course course) {this.course = course;}@ManyToOne@JoinColumn(name="student_id")public Student getStudent() {return student;}public void setStudent(Student student) {this.student = student;}}

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Course实体无关联注解。

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student跟course是多对多单向，student可访问course

student跟score是一对多双向

score跟course是多对一单向，score可访问course

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查找学生1所有课程的所有成绩：

public List<Score> findScoreByStudentId(Integer id) {List<Score> ls=em.createQuery("select score from Student s join s.scores score where s.id=:id")

                               .setParameter("id", id)

                               .getResultList();return ls;}

客户端：

                       ScoreDAO scoredao=(ScoreDAO)cxt.lookup("ScoreDAOBean/remote");List<Score> scores1=scoredao.findScoreByStudentId(new Integer(1));System.out.println("==查询学生1的所有科目成绩");for(Score s:scores1 ){System.out.println(s.getCourse().getName()+"--"+s.getScore());}

结果输出：

==查询学生1的所有科目成绩
course1--99.0
course2--98.0

sql输出：

22:21:07,765 INFO  [STDOUT] Hibernate: selectscores1_.id as id19_,scores1_.course_id as course4_19_,scores1_.student_id as student3_19_,scores1_.score as score19_ fromtb_student student0_ inner jointb_score scores1_ on student0_.id=scores1_.student_id wherestudent0_.id=?
22:21:07,765 INFO  [STDOUT] Hibernate: selectcourse0_.id as id18_0_,course0_.name as name18_0_,course0_.description as descript3_18_0_,course0_.optional as optional18_0_,course0_.teacher as teacher18_0_ fromtb_course course0_ wherecourse0_.id=?
22:21:07,765 INFO  [STDOUT] Hibernate: selectstudent0_.id as id20_1_,student0_.name as name20_1_,student0_.description as descript3_20_1_,student0_.class_id as class9_20_1_,student0_.temporary as temporary20_1_,student0_.age as age20_1_,student0_.sex as sex20_1_,student0_.birthday as birthday20_1_,student0_.createDate as createDate20_1_,classeo1_.id as id17_0_,classeo1_.classname as classname17_0_ fromtb_student student0_ left outer jointb_class classeo1_ on student0_.class_id=classeo1_.id wherestudent0_.id=?
22:21:07,781 INFO  [STDOUT] Hibernate: selectcourse0_.id as id18_0_,course0_.name as name18_0_,course0_.description as descript3_18_0_,course0_.optional as optional18_0_,course0_.teacher as teacher18_0_ fromtb_course course0_ wherecourse0_.id=?

默认及时加载？？？（不是对集合默认延迟加载吗？），JPQL将查询改为如下也可以：

public List<Score> findScoreByStudentId(Integer id) {List<Score> ls=em.createQuery("select s.scores from Student s  where s.id=:id")

                                 .setParameter("id", id)

                                 .getResultList();return ls;}

结果输出：

==查询学生1的所有科目成绩
course1--99.0
course2--98.0

输出的sql语句如下：

22:36:55,546 INFO  [STDOUT] Hibernate: selectscores1_.id as id19_,scores1_.course_id as course4_19_,scores1_.student_id as student3_19_,scores1_.score as score19_ fromtb_student student0_ inner jointb_score scores1_ on student0_.id=scores1_.student_id wherestudent0_.id=?
22:36:55,546 INFO  [STDOUT] Hibernate: selectcourse0_.id as id18_0_,course0_.name as name18_0_,course0_.description as descript3_18_0_,course0_.optional as optional18_0_,course0_.teacher as teacher18_0_ fromtb_course course0_ wherecourse0_.id=?
22:36:55,546 INFO  [STDOUT] Hibernate: selectstudent0_.id as id20_1_,student0_.name as name20_1_,student0_.description as descript3_20_1_,student0_.class_id as class9_20_1_,student0_.temporary as temporary20_1_,student0_.age as age20_1_,student0_.sex as sex20_1_,student0_.birthday as birthday20_1_,student0_.createDate as createDate20_1_,classeo1_.id as id17_0_,classeo1_.classname as classname17_0_ fromtb_student student0_ left outer jointb_class classeo1_ on student0_.class_id=classeo1_.id wherestudent0_.id=?
22:36:55,562 INFO  [STDOUT] Hibernate: selectcourse0_.id as id18_0_,course0_.name as name18_0_,course0_.description as descript3_18_0_,course0_.optional as optional18_0_,course0_.teacher as teacher18_0_ fromtb_course course0_ wherecourse0_.id=?