Display a single table for an embedded collection in JPA

Question

I have a rather unique situation when trying to map a single table to multiple objects in JPA. I read about @Embeddable and @ElementCollection, but I'm not sure how to use them in my situation (or, if possible). One database table contains course information. The table may contain rows in which everything in the course is the same, with the exception of several values, such as room number and day. For instance:

TERM_CODE   SUBJECT_CODE    ROOM    DAY    INSTRUCTOR_ID
201220      EGRE            0101    TR     123
201220      EGRE            0103    W      124

Is there a way in which I can extract data from two rows, as described above, and put the general data in one object and different values ​​in the Collection of separate objects? Here is an example of how I would like to define classes:

@Entity
public class Course implements Serializable {

    @Id
    @Column(name = "TERM_CODE")
    private Long termCode;

    @Column(name = "SUBJECT_CODE")
    private String subjectCode;

    @Embedded
    Collection<CourseSchedule> schedule;

    public Long getTermCode() {
     return termCode;
    }

    public void setTermCode(Long termCode) {
     this.termCode = termCode;
    }

    public String getSubjectCode() {
     return subjectCode;
    }

    public void setSubjectCode(String subjectCode) {
     this.subjectCode = subjectCode;
    }
}

CourseSchedule:

@Embeddable
public class CourseSchedule {
     private String room;
     private String day;

      public String getRoom() {
       return room;
      }

      public void setRoom(String room) {
       this.room = room;
      }

      public String getDay() {
       return day;
      }

      public void setDay(String day) {
       this.day = day;
      }

      public String getInstructorId() {
       return instructorId;
      }

      public void setInstructorId(String instructorId) {
       this.instructorId = instructorId;
      }
}

I am also confused about what my JPQL will look like in this situation as soon as I have matched them.

EDIT:

@Id TERM_CODE, Course Hibernate, CourseSchedule, , null.

2:

Course CourseSchedule ( ), @OneToMany @ManyToOne.

@Entity
@IdClass(CourseId.class)
@Table(name = "course_table")
public class Course implements Serializable {

    @OneToMany(mappedBy = "course")
    private Collection<CourseSchedule> schedule;

    @Id
    @Column(name = "TERM_CODE")
    private Long termCode;

    @Id
    @Column(name = "SUBJECT_CODE")
    private Long subjectCode;

    ...
}

@Entity
@IdClass(CourseScheduleId.class)
@Table(name = "course_table")
public class CourseSchedule implements Serializable {

    @ManyToOne
    @JoinColumns({
    @JoinColumn(name="TERM_CODE", referencedColumnName="TERM_CODE"),
    @JoinColumn(name = "SUBJECT_CODE", referencedColumnName="SUBJECT_CODE")
    })
    private Course course;

    @Column(name = "TERM_CODE")
    private Long termCode;

    @Column(name = "SUBJECT_CODE")
    private Long subjectCode;

    @Id
    private String room;

    @Id
    private String day;

    @Id
    @Column(name = "INSTRUCTOR_ID")
    private String instructorId;

    ...

}

(CourseId CourseScheduleId , ID.) :

org.hibernate.MappingException: Foreign key (FK82D03688F590EF27:course_table [TERM_CODE,SUBJECT_CODE])) must have same number of columns as the referenced primary key (course_table [ROOM,DAY,INSTRUCTOR_ID)

CourseSchedule, , .

? , ( ), - JPQL.

Answer 1

-, , , - setter setCourse CourseSchedule):

@Embeddable
public class Course implements Serializable {

@Column(name = "TERM_CODE")
private Long termCode;

@Column(name = "SUBJECT_CODE")
private String subjectCode;

@Transient
Collection<CourseSchedule> schedule = new ArrayList<CourseSchedule>();

public void setSchedule(Collection<CourseSchedule> schedule) {
    this.schedule = schedule;
}
public Collection<CourseSchedule> getSchedule() {
    return schedule;
}

public Long getTermCode() {
 return termCode;
 }

 public void setTermCode(Long termCode) {
 this.termCode = termCode;
 }

 public String getSubjectCode() {
return subjectCode;
 }

 public void setSubjectCode(String subjectCode) {
 this.subjectCode = subjectCode;
 }
}

CourseSchedule

@Entity(name="Course")
public class CourseSchedule {
private String room;
private String day;

@Id
@GeneratedValue
private int id;

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

@Embedded
private Course course;

public Course getCourse() {
    return course;
}

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

public String getRoom() {
    return room;
}

public void setRoom(String room) {
    this.room = room;
}

public String getDay() {
    return day;
}

public void setDay(String day) {
    this.day = day;
}
}

id    subject_code    term_code    day    room
1      "EGRE"           201220     "TR"   "0101"
2      "EGRE"           201220     "W"    "0103"

, . , , , , , - ...

Answer 2

( - ):

CourseSchedule , :

@Entity
@IdClass(CourseId.class)
@Table(name = "course_table")
public class Course implements Serializable {

    @Transient
    private Collection<CourseSchedule> schedule;

    @Id
    @Column(name = "TERM_CODE")
    private Long termCode;

    @Id
    @Column(name = "SUBJECT_CODE")
    private Long subjectCode;

    ...
}

@Entity
@IdClass(CourseScheduleId.class)
@Table(name = "course_table")
public class CourseSchedule implements Serializable {

    @Column(name = "TERM_CODE")
    private Long termCode;

    @Column(name = "SUBJECT_CODE")
    private Long subjectCode;

    @Id
    private String room;

    @Id
    private String day;

    @Id
    @Column(name = "INSTRUCTOR_ID")
    private String instructorId;

    ...

}

DAO Course CourseSchedule CourseSchedule :

public Collection<Course> getCourses() {
    String jpql = "SELECT DISTINCT course FROM Course course";

    TypedQuery<Course> typedQuery = entityManager
         .createQuery(jpql, Course.class);

    // get the Courses and set their schedules
    Collection<Course> courses = typedQuery.getResultList();
    setCourseSchedules(courses);

    return courses;
}

private void setCourseSchedules(Collection<Course> courses) {
    // query for getting CourseSchedules
    String jpql = "SELECT DISTINCT schedule FROM CourseSchedule schedule "
            + "WHERE schedule.subjectCode = :subjectCode "
            + "AND schedule.termCode = :termCode";

    for (Course c : courses) {
        TypedQuery<CourseSchedule> typedQuery = entityManager
                .createQuery(jpql, CourseSchedule.class)
                .setParameter("subjectCode", c.getSubjectCode())
                .setParameter("termCode", c.getTermCode());
        c.setSchedule(typedQuery.getResultList());
    }
}