About Question com.enthuware.ets.scbcd.v5.2.128 : test 2 question 22

[Alex]

Hi,
Considering the COUNT aggregate function the fourth proposition in this question (SELECT COUNT (s.presentations)...) suggests that we can uses collection_valued association path expression.
It is confirmed with Glassfish/toplink (IR). Furthermore If we read the persistence spec (JPA 1.0). p101 about COUNT, it seems to confirm this assertion : COUNT can use collection_valued association as argument, since there no detail.

But if we look at the definition of aggregate_expression in 4.4 section (BNF) or in the SELECT syntax p 99, it seems that only single_valued are permitted as association path expression. The book pro JPA 1.0 confirms this assertion. Tests with Hibernate (non IR) too.
Is there a GAP in the spec ?
So does COUNT accepts or not collection_valued association path expressions as argument ?


thanks by advance.
Best regards,
Alex

[admin]

The specification explicitly states, "The path expression argument to COUNT may terminate in
either a state field or a association field".

Obviously, COUNT wouldn't make much sense for a non-collection valued association. So I would say yes, COUNT accepts collection_valued association path expressions as an argument.

Did I understand your query correctly?

[Alex]

Hi,
Yes you have understood correctly my query and I agree with you for the spec. explanation (there is no detail about single-valued or collection-valued)
But what I say is that in the spec we can read too :

aggregate_expression ::=
{ AVG | MAX | MIN | SUM } ([DISTINCT] state_field_path_expression) |
COUNT ([DISTINCT] identification_variable | state_field_path_expression |
single_valued_association_path_expression)

Furthermore I don't find sample in the spec. with collection_valued associations.

And in EJB PRO JPA we can read : The count fonction take either identification variable or path expression...This path expression may resolve to state field or single valued association fields....

Regards,
Alex

[admin]

It could be an oversight on the part of Specification authors to miss collection valued association_path_expression.
I think so because logically, count(s.presentations) does make sense and it should be supported.