Is there such thing CASE expression in JPQL?

It has been added in JPA 2.0

Usage:

SELECT e.name, CASE WHEN (e.salary >= 100000) THEN 1 WHEN (e.salary < 100000) THEN 2 ELSE 0 END FROM Employee e

Ref: http://en.wikibooks.org/wiki/Java_Persistence/JPQL_BNF#New_in_JPA_2.0

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();

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)