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EJB-QL

sonali rao
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Joined: Nov 03, 2003
Posts: 64
Mock exam question :Why is the following EJB-QL statement wrong?
SELECT s.name FROM Student s, Program p where s.subjectid=p.subjectId
Sudhir V
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Joined: Dec 25, 2002
Posts: 143
Please provide some more details about the Student and Program tables.


Sudhir V<br />(SCJP 1.2, SCWCD, OCA, SCBCD)
Todor Mollov
Ranch Hand

Joined: Jan 13, 2004
Posts: 30
You cannot use JOINs in EJB-QL.
Sudhir V
Ranch Hand

Joined: Dec 25, 2002
Posts: 143
Hi Todor
Joins are allowed in EJB-QL. Please see the query in Pg233 of EJB Spec. Below is the query
SELECT DISTINCT OBJECT(o1) FROM Order o1, Order o2 WHERE o1.quantity > o2.quantity AND o2.customer.lastname = �Smith� AND o2.customer.firstname= �John�
[ February 29, 2004: Message edited by: Sudhir Vallam ]
Todor Mollov
Ranch Hand

Joined: Jan 13, 2004
Posts: 30
Hi Sudhir,
of course you are rigth but I was thinking in the context of the current thread.
So the question is : Why this EJB-QL is wrong
SELECT s.name FROM Student s, Program p where s.subjectid=p.subjectId

and the spec says on p.232
Because finder methods cannot return arbitrary types, the SELECT clause of an EJB QL query defined
for a finder method must always correspond to the abstract schema type of the entity bean for which the
finder method is defined.

and later on
In contrast, the SELECT clause of a query defined for a select method can
return the abstract schema types of other entity beans or the values of cmp-fields.

The given EJB-QL states that the method is select method (because of the return type), so it appeared that this EJB-QL is right.
 
 
subject: EJB-QL
 
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