4.5.3.2.1. Returned values
A query should return entities of the type which is specified at the moment of creating a datasource. In case of declarative creation, the entity type is specified in the class attribute of an XML element, if DsBuilder is used – in the setJavaClass() or setMetaClass() method.
For example, a query of the datasource of the Customer entity may look as follows:
select c from sales$Customer cor
select o.customer from sales$Order oA query cannot return single attributes or aggregates, for example:
select c.id, c.name from sales$Customer c /* invalid – returns single fields, not the whole Customer object */