About Question enthuware.oce-jpad.v6.2.580 :

[cliviu]

Hi Paul,

I use EclipseLink. You mean that is something wrong with the implementation ?

Thanks,
Liviu

[admin]

Hi Paul,

I use EclipseLink. You mean that is something wrong with the implementation ?

Thanks,
Liviu

That is certainly a possibility. We have seen several cases where implementation does not exactly comply with the specification. Let me confirm with the author on which implementation and version this was tested because there can differences because of versions as well.

I see that the explanation contains the query that gets generated, which aligns well with the API description. So I suspect that what you see is probably because of non compliant behavior.

HTH,
Paul.

[cliviu]

Hi Paul,
With JBoss I have 12 results , sounds right 2X6 ... with Eclipse Link only 2.

Nevertheless , in the explanation is given 2X3 results, which is correct only when the two users share the same three orders.
Please correct me if I'm wrong ...

Thanks,
Liviu

[admin]

Yes, you are right. It should be 12.
Paul.

[swiss-chris]

I'm a bit confused by the following explanation:

"2. In this case, you cannot join Customer with CustOrder (though the reverse is possible) because Customer does not have a Collection of CustOrders. (It is given in the problem statement that CustOrder to Customer is a unidirectional many to one relationship.)"

My SQL skills are probably a bit outdated, but in pure SQL, isn't it possible to join in either direction even on a unidirectional relationship?

In other words, can't I do

SELECT DISTINCT *
FROM Customer c
INNER JOIN CustOrder;

when only CustOrder has FK references to Customer?

Over at http://www.w3schools.com/sql/trysql.asp ... select_all I just tried:

SELECT DISTINCT *
FROM Customers c
JOIN Orders o ON o.CustomerID = c.CustomerID;

This worked fine, even though Orders is the owning side (FK from Orders pointing to PK of Customers)

If this is possible in MySQL, why does CriteryQuery [edit: replaced JPQL with CriteriaQuery, as this is what the exam question is about] care in which direction you specify the FROM and JOIN?

[admin]

Yes, it is certainly possible with pure sql but not with JPQL. JQPL traverses the object graph and builds sql querries off of that. So if there is no variable from A to B in A, it can't traverse from A to B.

[swiss-chris]

Yes, it is certainly possible with pure sql but not with JPQL. JQPL traverses the object graph and builds sql querries off of that. So if there is no variable from A to B in A, it can't traverse from A to B.

Thanks for your reply!
I just realized that I meant CriteriaQuery, not JPQL. How does it work with CriteriaQuery? Where can I find this behavior documented in the specification?

[admin]

Same thing with CriterialQuery as well. You can go through the specification for more details.

[romsky]

I think the explanation for 4th option has to go to the first one.

[admin]

It looks ok. Explanation to option 4 gives 2 reasons why it is incorrect. Option 1 is correct anyway.