Subselect in ReportQuery

Question

Hi,
(first time post, please move if appropriate)
I can find lots of information in the Toplink docs and elsewhere about using sub queries in the selection criteria of a ReportQuery, but not as an attribute. Here's what I'm trying to do:
I have two tables, SUPPLIER and DOCUMENT. I'm trying to get various values from the SUPPLIER table, and a count from the DOCUMENT table, for a given SUPPLIER ID. That is, some data about the supplier, and the number of documents he/she has. In SQL I would do:
SELECT COLUMNA, COLUMNB, (SELECT COUNT(*) FROM DOCUMENT WHERE DOCUMENT.SUPPLIER_ID = 123) FROM SUPPLIER WHERE SUPPLIER_ID = 123
which seems to work. But, as a ReportQuery, I'm having trouble, here's what I'm doing:
ExpressionBuilder exp = new ExpressionBuilder();
ReportQuery query = new ReportQuery(exp);
ExpressionBuilder equalOppsBuilder = new ExpressionBuilder(Document.class);
ReportQuery equalOppsQuery = new ReportQuery(equalOppsBuilder);
equalOppsQuery.setReferenceClass(Document.class);
equalOppsQuery.addCount("count", equalOppsBuilder.get("SUPPLIER_ID"));
equalOppsQuery.setSelectionCriteria(equalOppsBuilder.get("SUPPLIER_ID").equal(getSupplierId()));
query.addAttribute("equalOppsCount", expBuilder.subQuery(equalOppsQuery));
With the code between the ...'s above commented out, my query works correctly. With it in, I get a java.lang.NumberFormatException.
Digging a little deeper, I see that the query being sent to the database (according to the logs) doesn't actually include the sub select at all. It seems that once the query is returned, Toplink is expecting the result, and the columns following the position of the subselect are being put in the wrong place.
The following 5 columns are numbers, the 6th being text. It seems that the NumberFormatException is caused by Toplink trying to parse the text value as a number. Commenting out that line causes the same problem further down, with another text value that follows a number. Further, removing that line (and, similarly, putting the subselect as the last attribute in the query), gives me an oracle.toplink.exceptions.QueryException:
Exception Description: ReportQuery result size mismatch. Expecting [51], but retrieved [51]
I've tried various different combinations of the code above, doing the subselect, such as just using equalOppsQuery.addCount() without parameters, using addMaximum() instead, and using query.addItem() instead of addAttribute(), none of which has made a difference.
Perhaps there's something obvious that I'm getting wrong...? Any pointers gratefully appreciated.

Answer 1

TopLink ReportQuery does not support sub-selects in the from SELECT clause. If you require this you will need to use custom SQL.
You may be able to define the same query using a group-by however.
(you may need to group-by each field your select, but should still get correct result).
For the NumberFormatException and the QueryException could you include the stack trace.
-- James : http://www.eclipselink.org