Question

I am new to JPA. So my question should be so simple to some.

Below is the Simple Query in SQL which i would like to convert to JPA. I already have an entity class called TimeEnt.

SELECT 
     SUM(TimeEntryActualHours) as UnBilledHrs,
     SUM (TimeEntryAmount) as UnbilledAmount
FROM TimeEnt WHERE MatterID = 200

Answer 1

The JPA Query Language does support aggregates functions in the SELECT clause like AVG, COUNT, MAX, MIN, SUM and does support multiple select_expressions in the SELECT clause, in which case the result is a List of Object array (Object[]). From the JPA specification:

4.8.1 Result Type of the SELECT Clause

…

The result type of the SELECT
clause is defined by the the result
types of the select_expressions
contained in it. When multiple
select_expressions are used in the
SELECT clause, the result of the query
is of type Object[], and the
elements in this result correspond in
order to the order of their
specification in the SELECT clause
and in type to the result types of
each of the select_expressions.

In other words, the kind of query you mentioned in a comment (and since you didn’t provide your entity, I’ll base my answer on your example) is supported, no problem. Here is a code sample:

String qlString = "SELECT AVG(x.price), SUM(x.stocks) FROM Magazine x WHERE ...";
Query q = em.createQuery(qlString);
Object[] results = (Object[]) q.getSingleResult();

for (Object object : results) {
    System.out.println(object);
}

References

• JPA 1.0 Specification
  • 4.8.1 Result Type of the SELECT Clause
  • 4.8.4 Aggregate Functions in the SELECT Clause