Is there such thing CASE expression in JPQL?

Let say there is a table:

TableA:Field1, Field2, Field3

and associated JPA entity class

@Entity
@Table(name="TableA")
public class TableA{
  @Id
  @Column(name="Field1")
  private Long id;

  @Column(name="Field2")
  private Long field2;

  @Column(name="Field3")
  private Long field3;

  //... more associated getter and setter...
}

Is there any way to construct a JPQL statement that loosely translated to this SQL, ie how to translated the case expression to JPQL?

select field1,
case
  when field2 = 1 then 'One'
  when field2 = 2 then 'Two'
  else 'Other number'
end,
field3
from tableA;

From stackoverflow

• Looking over the Java Persistence API it doesn't appear to have a construct for this. It looks like you're going to need a special getter function which will do the CASE statement functionality.

  Nordin : Thanks for the reply. I am not trying it yet, but, I wonder if the said getter can be used in a JPQL?

• You can use the event listeners provided by Jpa to do something when you load one row of the db, ie:

  @Entity
  @Table(name = "TableA")
  public class TableA {
  
      @Id
      @Column(name = "Field1")
      private Long id;
  
      @Column(name = "Field2")
      private Long field2;
  
      @Column(name = "Field3")
      private Long field3;
  
      // ... more associated getter and setter...
  
      @Transient
      private String field4;
  
      @PostLoad
      private void onLoad() {
          if (field2 != null) {
              switch (field2.intValue()) {
              case 1:
                  field4 = "One";
                  break;
              case 2:
                  field4 = "Two";
                  break;
              default:
                  field4 = "Other Number";
                  break;
              }
          }
      }
  }
  

  (the field4 not persist in the db)

  (take this like an workaround to "non implemented feature in JPA" like case statements)

• Did this solution work for anyone? It's not working for me. I'm using Eclipselink and I get the following error: unknown state or association field [simplifiedSideString] of class [com.entity.Trade]. Trade is the entity and simplifiedSideString is the @Transient field equivalent to field4 in the above example. To the extent of my knowledge, transient fields cannot be used in JPQL queries or at least I didn't succeed in using any yet.

• There is certainly such thing in Hibernate so when you use Hibernate as your JPA provider then you can write your query as in this example:

      Query query = entityManager.createQuery("UPDATE MNPOperationPrintDocuments o SET o.fileDownloadCount = CASE WHEN o.fileDownloadCount IS NULL THEN 1 ELSE (o.fileDownloadCount + 1) END " +
                                              " WHERE o IN (:operations)");
      query.setParameter("operations", mnpOperationPrintDocumentsList);
  
      int result = query.executeUpdate();