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JPA - Using multiple instances of the same embeddable having relationship with another entity

[Updated: May 31, 2017, Created: May 20, 2017]

Multiple instances of the same embeddable class can be embedded in the same entity. We saw in this example how to resolve conflicting column names by using @AttributeOverrides and @AttributeOverride annotations. In case if the target embeddable class has an association with another entity then there will be join column name conflict as well; to resolve that conflict, we need to use @AssociationOverrides and @AssociationOverride annotations. Let's see an example how to do that.

Example

Following embeddable class has ManyToOne relationship with EntityB:

@Embeddable
public class ClassA {
  private String myStr;

  @ManyToOne
  private EntityB entityBRef;
    .............
}
@Entity
public class EntityB {
  @Id
  @GeneratedValue
  private int myIdB;
  private String myStr2;
    .............
}

EntityA is using multiple instances of embeddable ClassA. This class needs to resolve all conflicting column names:

@Entity
public class EntityA {
  @Id
  @GeneratedValue
  private int id;

  @Embedded
  @AttributeOverrides({
          @AttributeOverride(name = "myStr", column = @Column(name = "MY_STR_COL1"))
  })
  @AssociationOverrides({
          @AssociationOverride(
                  name = "entityBRef", joinColumns = @JoinColumn(name = "EntityAB_JOIN1"))
  })
  private ClassA classARef;

  @Embedded
  @AttributeOverrides({
          @AttributeOverride(name = "myStr", column = @Column(name = "MY_STR_COL2"))
  })
  @AssociationOverrides({
          @AssociationOverride(
                  name = "entityBRef", joinColumns = @JoinColumn(name = "EntityAB_JOIN2"))
  })
  private ClassA classARef2;
    .............
}
public class ExampleMain {

      public static void main(String[] args) {
      EntityManagerFactory emf = Persistence.createEntityManagerFactory("example-unit");
      try {
          EntityManager em = emf.createEntityManager();
          nativeQuery(em, "SHOW TABLES");
          nativeQuery(em, "SHOW COLUMNS from EntityA");
          nativeQuery(em, "SHOW COLUMNS from EntityB");
          emf.close();
      } finally {
          emf.close();
      }
  }

  public static void nativeQuery(EntityManager em, String s) {
      System.out.printf("'%s'%n",  s);
      Query query = em.createNativeQuery(s);
      List list = query.getResultList();
      for (Object o : list) {
          if(o instanceof Object[]) {
              System.out.println(Arrays.toString((Object[]) o));
          }else{
              System.out.println(o);
          }
      }
  }
}

Output

'SHOW TABLES'
[ENTITYA, PUBLIC]
[ENTITYB, PUBLIC]
'SHOW COLUMNS from EntityA'
[ID, INTEGER(10), NO, PRI, NULL]
[MY_STR_COL1, VARCHAR(255), YES, , NULL]
[MY_STR_COL2, VARCHAR(255), YES, , NULL]
[ENTITYAB_JOIN1, INTEGER(10), YES, , NULL]
[ENTITYAB_JOIN2, INTEGER(10), YES, , NULL]
'SHOW COLUMNS from EntityB'
[MYIDB, INTEGER(10), NO, PRI, NULL]
[MYSTR2, VARCHAR(255), YES, , NULL]

Persisting and loading data

public class ExampleMain2 {

  public static void main(String[] args) {
      EntityManagerFactory emf = Persistence.createEntityManagerFactory("example-unit");
      try {
          persistEntity(emf);
          runNativeQueries(emf);
          loadEntity(emf);
      } finally {
          emf.close();
      }
  }

  private static void persistEntity(EntityManagerFactory emf) {
      System.out.println("-- Persisting entities --");
      EntityManager em = emf.createEntityManager();

      EntityB entityB = new EntityB();
      entityB.setMyStr2("a test string in EntityB");

      ClassA a = new ClassA();
      a.setMyStr("a test string in ClassA");
      a.setEntityBRef(entityB);

      EntityB entityB2 = new EntityB();
      entityB2.setMyStr2("a test string in EntityB 2");

      ClassA a2 = new ClassA();
      a2.setMyStr("a test string in ClassA 2");
      a2.setEntityBRef(entityB2);

      EntityA entityA = new EntityA();
      entityA.setClassARef(a);
      entityA.setClassARef2(a2);

      System.out.println(entityA);

      em.getTransaction().begin();
      em.persist(entityA);
      em.persist(entityB);
      em.persist(entityB2);
      em.getTransaction().commit();
      em.close();
  }

  private static void runNativeQueries(EntityManagerFactory emf) {
      System.out.println("-- native queries --");
      EntityManager em = emf.createEntityManager();
      ExampleMain.nativeQuery(em, "Select * from EntityA");
      ExampleMain.nativeQuery(em, "Select * from EntityB");
  }

  private static void loadEntity(EntityManagerFactory emf) {
      System.out.println("-- Loading EntityA --");
      EntityManager em = emf.createEntityManager();
      List<EntityA> entityAList = em.createQuery("Select t from EntityA t")
                                    .getResultList();
      entityAList.forEach(System.out::println);

      System.out.println("-- Loading EntityB --");
      List<EntityB> entityBList = em.createQuery("Select t from EntityB t")
                                    .getResultList();
      entityBList.forEach(System.out::println);
      em.close();
  }
}

Output

-- Persisting entities --
EntityA{id=0, classARef=ClassA{myStr='a test string in ClassA', entityBRef=EntityB{myIdB=0, myStr2='a test string in EntityB'}}, classARef2=ClassA{myStr='a test string in ClassA 2', entityBRef=EntityB{myIdB=0, myStr2='a test string in EntityB 2'}}}
-- native queries --
'Select * from EntityA'
[1, a test string in ClassA, a test string in ClassA 2, 2, 3]
'Select * from EntityB'
[2, a test string in EntityB]
[3, a test string in EntityB 2]
-- Loading EntityA --
EntityA{id=1, classARef=ClassA{myStr='a test string in ClassA', entityBRef=EntityB{myIdB=2, myStr2='a test string in EntityB'}}, classARef2=ClassA{myStr='a test string in ClassA 2', entityBRef=EntityB{myIdB=3, myStr2='a test string in EntityB 2'}}}
-- Loading EntityB --
EntityB{myIdB=2, myStr2='a test string in EntityB'}
EntityB{myIdB=3, myStr2='a test string in EntityB 2'}

org.hibernate.MappingException: Repeated column in mapping

If we don't use @AssociativeOverrides then we will have MappingException. Let's check that out:

@Entity
public class EntityA {
  @Id
  @GeneratedValue
  private int id;

   @Embedded
    @AttributeOverrides({
            @AttributeOverride(name = "myStr", column = @Column(name = "MY_STR_COL1"))
    })
 /*   @AssociationOverrides({
            @AssociationOverride(
                    name = "entityBRef", joinColumns = @JoinColumn(name = "EntityAB_JOIN1"))
    })*/
    private ClassA classARef;

    @Embedded
    @AttributeOverrides({
            @AttributeOverride(name = "myStr", column = @Column(name = "MY_STR_COL2"))
    })
   /* @AssociationOverrides({
            @AssociationOverride(
                    name = "entityBRef", joinColumns = @JoinColumn(name = "EntityAB_JOIN2"))
    })*/
    private ClassA classARef2;
    .............
}

Output

On running ExampleMain, we will have following output

Caused by: org.hibernate.MappingException: Repeated column in mapping for entity: com.logicbig.example.EntityA column: entityBRef_myIdB (should be mapped with insert="false" update="false")
	at org.hibernate.mapping.PersistentClass.checkColumnDuplication(PersistentClass.java:835)
	at org.hibernate.mapping.PersistentClass.checkPropertyColumnDuplication(PersistentClass.java:853)    ........................

Example Project

Dependencies and Technologies Used:

  • h2 1.4.193: H2 Database Engine.
  • hibernate-core 5.2.8.Final: The core O/RM functionality as provided by Hibernate.
    Implements javax.persistence:javax.persistence-api version 2.1
  • JDK 1.8
  • Maven 3.3.9

Override Embeddable Association Select All Download
  • embeddable-multiple-instances-with-relationship
    • src
      • main
        • java
          • com
            • logicbig
              • example
                • EntityA.java
          • resources
            • META-INF

    See Also