How to get Column names of JPA entity

Question

All my JPA entity classes implement an interface called Entity which is defined like this:

public interface Entity extends Serializable {
// some methods

}

Some of the fields of my JPA entity have @Column annotation on top of them and some don't. MyEntity class is defined like below:

@Entity
public class MyEntity implements Entity {

   @Id
   private Long id; // Assume that it is auto-generated using a sequence. 

   @Column(name="field1")
   private String field1;


   private SecureString field2; //SecureString is a custom class

   //getters and setters

}

My delete method accepts an Entity.

@Override
public void delete(Entity baseEntity) {

   em.remove(baseEntity); //em is entityManager
}

Whenever the delete method is invoked I want three things inside my delete method:

1) Fields of MyEntity that are of type SecureString

2) Column name of that particular field in DB (The field may or may not have @Column annotation)

3) The value of id field

Note that when the delete() method is invoked, we don't know for which entity it is invoked, it may be for MyEntity1 , MyEntity2 etc.

I have tried doing something like below:

for (Field field : baseEntity.getClass().getFields()) {
    if (SecureString.class.isAssignableFrom(field.getType())) {
        // But the field doesn't have annotation @Column specified
        Column column = field.getAnnotation(Column.class);

        String columnName = column.name();
    }
}

But this will only work if the field has @Column annotation. Also it doesn't get me other two things that I need. Any ideas?

Answer 1

Hibernate can use different naming strategies to map property names, which are defined implicitly (without @Column(name = "...")). To have a 'physical' names you need to dive into Hibernate internals. First, you have to wire an EntityManagerFactory to your service.

@Autowired
private EntityManagerFactory entityManagerFactory;

Second, you have to retrieve an AbstractEntityPersister for your class

    SessionFactory sessionFactory = entityManagerFactory.unwrap(SessionFactory.class);
    AbstractEntityPersister persister = ((AbstractEntityPersister)sessionFactory.getClassMetadata(baseEntity.getClass()));

Third, you're almost there with your code. You just have to handle both cases - with and without @Column annotation. Try this:

for (Field field : baseEntity.getClass().getFields()) {
    if (SecureString.class.isAssignableFrom(field.getType())) {
        String columnName;
        if (field.isAnnotationPresent(Column.class)) {
            columnName = field.getAnnotation(Column.class).name();
        } else {
            String[] columnNames = persister.getPropertyColumnNames(field.getName());
            if (columnNames.length > 0) {
                columnName = columnNames[0];
            }
        }
    }
}

Note that getPropertyColumnNames() retrieves only 'property' fields, that are not a part of primary key. To retrieve key column names, use getKeyColumnNames() .

And about id field. Do you really need to have all @Id's in child classes? Maybe would better to move @Id to Entity class and mark this class with @MappedSuperclass annotation? Then you can retrieve it just with baseEntity.getId();