CODEWITHSUNDEEP
hibernatehibernate-mapping
Shvalb
Shvalb

Reputation: 1933

Hibernate: Mapping Multi-Rows with ElementCollection - Single table no Embeddable

Looking for a solution to map multiple student_id rows under the same class_id, here is the table which has 3 fields:

integer id PRIMARY KEY
integer class_id;
integer student_id;

The table can have multiple rows under the same class_id like this:

Table = 'class'
id  class_id  student_id 
1,    1,          1
2,    1,          2
3,    1,          3
4,    2,          1
5,    3,          1

I'm trying to Map this into a Pojo so I can use it as follow:

List<UniClass> uniClasses = session.createQuery("FROM ClassOfStudent", ClassOfStudent.class).getResultList();

I'm trying to solve this problem by using @ElementCollection

Here is my attempt:

@Entity
@Table(name = "class")
public class ClassOfStudents{
   @Id
   @Column("id")
   private long m_id;

   @Column(name = "class_id")
   private long m_classId;

   @ElementCollection
   @CollectionTable(name = "class", joinColumns = @JoinColumn(name="class_id"))
   @Column(name = "student_id")
   private List<Long> m_studentIds;

   ....
}

Any idea how to make this work?

Upvotes: 0

Views: 256

Answers (1)

Shvalb
Shvalb

Reputation: 1933

The trick that made this possible is that eventually I mapped the @Id of the class to be m_classId although it's not really the primary key of the table in the DB.

@Entity
@Table(name = "class")
public class ClassOfStudents implements Serializable
{
  @Id
  @Column(name = "class_id")
  private long classId;

  @ElementCollection(targetClass = Long.class, fetch = FetchType.EAGER)
  @CollectionTable(name = "class", joinColumns = @JoinColumn(name = "class_id"))
  @Column(name = "student_id", nullable = false)  
  private List<Long> m_studentIds;
...
}

Upvotes: 0

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