EclipseLink native query result into POJO - Missing descriptor for [Class]

Question

I'm using EclipseLink to run some Native SQL. I need to return the data into a POJO. I followed the instructions at EclipseLink Docs, but I receive the error Missing descriptor for [Class]

The query columns have been named to match the member variables of the POJO. Do I need to do some additional mapping?

POJO:

public class AnnouncementRecipientsFlattenedDTO {

        private BigDecimal announcementId;
        private String recipientAddress;
        private String type;

        public AnnouncementRecipientsFlattenedDTO() {
            super();
        }

        public AnnouncementRecipientsFlattenedDTO(BigDecimal announcementId, String recipientAddress, String type) {
            super();
            this.announcementId = announcementId;
            this.recipientAddress = recipientAddress;
            this.type = type;
        }

    ... Getters/Setters

Entity Manager call:

public List<AnnouncementRecipientsFlattenedDTO> getNormalizedRecipientsForAnnouncement(int announcementId) {
    Query query = em.createNamedQuery(AnnouncementDeliveryLog.FIND_NORMALIZED_RECIPIENTS_FOR_ANNOUNCEMENT, AnnouncementRecipientsFlattenedDTO.class);
    query.setParameter(1, announcementId);
    return query.getResultList();
}

Answer 1

Had the same kind of problem where I wanted to return a List of POJOs, and really just POJOs (call it DTO if you want) and not @Entity annotated Objects.

class PojoExample {

  String name;

  @Enumerated(EnumType.STRING)
  SomeEnum type;

  public PojoExample(String name, SomeEnum type) {
    this.name = name;
    this.type = type;
  }
}

With the following Query:

String query = "SELECT b.name, a.newtype as type FROM tablea a, tableb b where a.tableb_id = b_id";

Query query = getEntityManager().createNativeQuery(query, "PojoExample");

@SuppressWarnings("unchecked")
List<PojoExample> data = query.getResultList();

Creates the PojoExample from the database without the need for an Entity annotation on PojoExample. You can find the method call in the Oracle Docs here.

edit: As it turns out you have to use @SqlResultSetMapping for this to work, otherwise your query.getResultList() returns a List of Object.

@SqlResultSetMapping(name = "PojoExample", 
  classes = @ConstructorResult(columns = {
    @ColumnResult(name = "name", type = String.class), 
    @ColumnResult(name = "type", type = String.class)
  }, 
  targetClass = PojoExample.class)
 )

Just put this anywhere under your @Entity annotation (so in this example either in tablea or tableb because PojoExample has no @Entity annotation)

Answer 2

Also, don't forget to add in your POJO class in persistence.xml! It can be easy to overlook if you are used to your IDE managing that file for you.

Answer 3

Old question but may be following solution will help someone else.

Suppose you want to return a list of columns, data type and data length for a given table in Oracle. I have written below a native sample query for this:

  private static final String TABLE_COLUMNS = "select utc.COLUMN_NAME, utc.DATA_TYPE, utc.DATA_LENGTH "
        + "from user_tab_columns utc "
        + "where utc.table_name = ? "                
        + "order by utc.column_name asc";

Now the requirement is to construct a list of POJO from the result of above query.

Define TableColumn entity class as below:

@Entity
public class TableColumn implements Serializable {

@Id
@Column(name = "COLUMN_NAME")
private String columnName;
@Column(name = "DATA_TYPE")
private String dataType;
@Column(name = "DATA_LENGTH")
private int dataLength;

public String getColumnName() {
    return columnName;
}

public void setColumnName(String columnName) {
    this.columnName = columnName;
}

public String getDataType() {
    return dataType;
}

public void setDataType(String dataType) {
    this.dataType = dataType;
}

public int getDataLength() {
    return dataLength;
}

public void setDataLength(int dataLength) {
    this.dataLength = dataLength;
}

public TableColumn(String columnName, String dataType, int dataLength) {
    this.columnName = columnName;
    this.dataType = dataType;
    this.dataLength = dataLength;
}

public TableColumn(String columnName) {
    this.columnName = columnName;
}

public TableColumn() {
}

@Override
public int hashCode() {
    int hash = 0;
    hash += (columnName != null ? columnName.hashCode() : 0);
    return hash;
}

@Override
public boolean equals(Object object) {

    if (!(object instanceof TableColumn)) {
        return false;
    }
    TableColumn other = (TableColumn) object;
    if ((this.columnName == null && other.columnName != null) || (this.columnName != null && !this.columnName.equals(other.columnName))) {
        return false;
    }
    return true;
}

@Override
public String toString() {
    return getColumnName();
}

}

Now we are ready to construct a list of POJO. Use the sample code below to construct get your result as List of POJOs.

public List<TableColumn> findTableColumns(String table) {
    List<TableColumn> listTables = new ArrayList<>();
    EntityManager em = emf.createEntityManager();
    Query q = em.createNativeQuery(TABLE_COLUMNS, TableColumn.class).setParameter(1, table);
    listTables = q.getResultList();
    em.close();
    return listTables;
}

Answer 4

I found out you can put the results of a Native Query execution into a List of Arrays that hold Objects. Then one can iterate over the list and Array elements and build the desired Entity objects.

List<Object[]> rawResultList;

    Query query =
        em.createNamedQuery(AnnouncementDeliveryLog.FIND_NORMALIZED_RECIPIENTS_FOR_ANNOUNCEMENT);
    rawResultList = query.getResultList();

    for (Object[] resultElement : rawResultList) {
        AnnouncementDeliveryLog adl = new AnnouncementDeliveryLog(getAnnouncementById(announcementId), (String)resultElement[1], (String)resultElement[2], "TO_SEND");
        persistAnnouncementDeliveryLog(adl);
    }

Answer 5

You can only use native SQL queries with a class if the class is mapped. You need to define the AnnouncementRecipientsFlattenedDTO class as an @Entity.

Otherwise just create the native query with only the SQL and get an array of the data back and construct your DTO yourself using the data.